The dangers of forcefully unwrapping values

Whenever I’m programming, I have a goal in mind, generally a problem to solve. I want my solutions to be simple, yet elegant and reliable. Thankfully, Swift is a great language for this. The language is safe, its syntax is beautiful with great readability. The way Swift handles nullability contributes greatly to its safety.

If you want to declare a variable in Swift you can use either the let or var keyword. If you don’t want to assign a value to one of your properties right away you could write something like var episodeName: String?. This informs the Swift compiler that episodeName might not have a value when we’re accessing it. If we don’t add the question mark and write var episodeName: String, the episodeName will need to be assigned a value when we initialize the object that contains this property. A third way to declare episodeName is to implicitly unwrap the value: var episodeName: String!. This tells the compiler that we are 100% sure that episodeName will get a value before we attempt to access it.

These question mark / exclamation mark semantics also apply to using variables in your code. When you’ve declared your variable with a questionmark (var episodeName: String?) we are never sure if episodeName is nil or a String. So whenever we want to use this variable we need to unwrap it. The safest way to do this is as follows:

However, if you’re 100% sure you’ve set a value, you can tell the Swift compiler to stop complaining because you know what you’re doing and you just want to get your episode’s name:

By adding the exclamation mark after episodeName, we force unwrapping it and we can use it’s value straight away without an extra if statement.

Where’s the danger?

If you’re writing an application you’re sometimes sure that you assign a value to something. For example, you might have written something like:

This code should usually be safe. Before we ask the show for it’s episodeName we actually set it so we’re always sure that episodeName has a value before we access it. So the implementation of printEpisodeName might be:

This shouldn’t throw errors. After all, we know what we’re doing! We always set the episodeName right after we instantiate our class. What could go wrong, right? Well… besides the fact that we probably should have created an initializer that takes the episodeName, a lot can go wrong.

Honeymoon’s over..

So, our project has been ongoing for a few weeks and we’re changing the API. Before, we were guaranteed that the API would always return properly formatted JSON but we’ve decided that things like the name for an episode isn’t guaranteed anymore. In other words, the name can be nil.
We test our app, everything still works when we’re navigation to our show page so we’re happy. But then.. crash reports come in. Users are livid and to add insult to injury, your manager is suddenly next to your desk. The app is crashing. Hard.

What’s going on!? Everything was fine before! So we start searching and debugging. And once we manage to reproduce the error we see what’s going on:

And then we remember. The forcefully unwrapped optional in our TVShow class:

When we set the episodeName on our tv show, the name we get from the API can be nil. And that’s alright because we declared our episodeName like this: var episodeName: String?. Which means that episodeName can be either nil or a String. Luckily, our bug is easily fixed:

Now we handle the optional value properly, we avoid crashes and an angry manager. Time to get yourself a cup of coffee and tell your manager that you’ve fixed the error.

The takeaway :)

As we saw in this post it can be tempting to force the unwrappin of a variable when we’re pretty sure that we will set it before we use it. But as requirements change it can be easy to overlook situations where a variable can suddenly be nil when we try to access it.

My advice is to (almost) always unwrap optionals properly with an if let construction. It’s the only way to be 100% sure that you’re not accidentally accessing a variable whose value is actually nil. More importantly, this will help to prevent future crashes.

So remember kids, always unwrap your optionals in a safe way.

High performance shadows for UIView

No app is truly complete without some subtle shadows. Especially now that Google’s Material Design is showing us that shadows are cool again we need a way to properly add them in our apps. In my previous post I wrote about a way to create a custom UICollectionView layout. There was one problem with that post though, that shadows are incredibly heavy on the iPhone and scrolling stutters.

So can we fix this? The answer is yes and the solution is (surprisingly) easy. A Google search led me to this Stackoverflow question about shadows. The solution I tried first was to simple rasterize my layer but that wasn’t what I was looking for. Images started to look very bad and I didn’t want that. Another solution that was proposed is to supply the  layer with a  shadowPath.

What is shadowPath and what does it do?

If you set the  shadowPath property it will function as a guide to the shadow that ends up underneath your view. If you don’t set this, the view need to be analyzed at runtime to determine where the view is transparent and where it isn’t which will result in the eventual shadow shape. This is a pretty costly operation, especially if you do this for about 20 views at a time in a UICollectionView. And even more so if you start scrolling in this view.

Implementing shadowPath

Assuming we’re using the code from my previous post there isn’t much we have to do. We have to create a circular path that has the same size as the imageView. We know that our  imageView get’s rendered at 80px by 80px so we can use  UIBezierPath with rounded corners to generate a circular path. Let’s add this line before we specify the shadows in the  CustomCollectionViewCell class:

Build and run the project and you should now see butter smooth scrolling instead of the bad scrolling we had before.


If you want to use shadows on your views then you should probably also set the  shadowPath on your view to ensure proper performance. By doing this you can speed up rendering a great deal because otherwise the view will be analyzed at runtime to find out what shape the view has, this is a lot slower than just providing the proper shadow path. Setting the path does not only increase performance but it also allows you to create many fun effects with shadows.

Creating a custom UICollectionViewLayout in Swift

If you’ve ever built an iOS app that uses some kind of grid layout or displays a list in a way that doesn’t fit a UITableView you have probably used a UICollectionView. This components allows for very simple grid layout creation and it even allows you to dynamically change layouts. This component becomes even more powerful and flexible if you create your own layout by subclassing UICollectionViewLayout.

Recently I had to build a kind of playful, almost grid like layout. To me this seemed like the best time to dive straight into subclassing the UICollectionViewLayout and create a nice layout. In this post I will explain how I did it and I’ll provide you with a little bit of code so you can start building your own layouts in no-time.

The end result

Since I’m a great fan of cats, we’ll be building a collection of cat images. The images will be rounded, they’ll have a nice shadow so they look kind of nice and the magic bit is, of course, the slightly offset rows that we could realize because we’re using a custom UICollectionViewLayout.

Schermafbeelding 2015-07-07 om 20.57.24The image above illustrates what we’ll end up with when we’re done. It’s amazing, isn’t it?

Initial set-up

Before we get to build our layout we have to do some set up. I created a new XCode project and selected the Single View Application template. I named my project “CustomCollectionViewLayout” because I’m not very good at coming up with names. You can name your project anything you like.

Step one: setting up the interface

Creating the UICollectionView

The first thing you should do is open up the Main.storyboard and drag a UICollectionView out to your View Controller. When you’ve done this give the UICollectionView a white background color and add constraints to it so it will fit your view nicely. If you’re unsure how to do this, size the UICollectionView so that it touches the left, bottom and right edges of the view and it should be aligned underneath the status bar. XCode should provide you with some helpful guides for this. Once your view is sized like this, click in the bottom right corner of your canvas and choose “Reset to suggested constraints”.

Schermafbeelding 2015-07-07 om 21.07.21

Next up, we should connect our UICollectionView to our ViewController class. Open up the assistant editor by pressing the two overlapping circles in your XCode window and make sure that the editor is set automatically use an appropriate file.

Schermafbeelding 2015-07-07 om 21.25.52

Select the UICollectionView, hold ctrl and drag over to the code editor to create an outlet for the UICollectionView. I named mine “collectionView”. That’s all setup we need for now.

Creating a UICollectionViewCell

To display our cat images we need to have a UICollectionViewCell with an image inside of it. To do this we can simply create our own UICollectionViewCell and put a UIImageView inside of it.

First, create a new CocoaTouch Class (either press cmd+n or by navigating through the file menu). Name your file CustomCollectionViewCell, make it subclass UICollectionViewCell and check “Also create xib file”.

Schermafbeelding 2015-07-07 om 21.14.25

XCode should have created a .swift and .xib file for you. Let’s open up the .xib file first and then press the assistant editor button so we have both the .xib and .swift file open at the same time. Drag a UIImageView out into your custom cell and size it so that it fill up the cell exactly. Since we’ll be resizing the cell later we should “Reset to suggested constraints” again, just like we did with the UICollectionView earlier. Now select the image, press and hold ctrl and then drag to your swift file to create an outlet for the imageView. I named mine “imageView”.

Our example image had rounded corners and a shadow applied so let’s write some code to make this happen. All you need is a few lines inside  awakeFromNib().

This code is fairly straightforward. First we apply rounded corners to our imageView. Then we apply a shadow to the cell itself. You can tweak the numbers to change how the cell looks. Did you notice the magic number  40? In an actual app you might want to find a better solution for this because 40 is half of the cell’s eventual size but there’s no way to know that unless you came up with all the sizings yourself.

The last thing we have to do is register this custom cell to our UICollectionView. We created an IBOutlet for the UICollectionView earlier by ctrl+dragging from the UICollectionView to the ViewController. Open up  ViewController.swift  and add this line to the  viewDidLoad method:

We’re using a  cellIdentifier  variable here, let’s define that as well. Place this code right below your collectionView  outlet:

Allright, that’s all. Our UI is fully prepared now. The code you’ve added to ViewController.swift  should look like this:

Step two: setting up the UICollectionView dataSource

To get our UICollectionView to display our collection of cat pictures we will need to make sure our UICollectionView knows where to go for it’s data. To do this, select the connections inspector in the right drawer of XCode and drag the dataSource connector to the ViewController class.

To actually implement the dataSource we should make our ViewController  comply to the UICollectionViewDataSource  protocol. Open up  ViewController.swift  and change it’s class definition to this:

By adding  UICollectionViewDataSource  after the superclass we tell Swift that this class implements the  UICollectionViewDataSource protocol. This protocol dictates that we should at least provide our UICollectionView with:

  • the amount of sections it should contain
  • the amount of items there are in each sections
  • cells to display

The following code takes care of all this:

Our collection will contain a single section with 50 items. Our cell creation code is also fairly straightforward, we dequeue the cell that we’ve registered earlier and we forcefully cast it to be a  CustomCollectionViewCell. Then we set the  imageView.image to one of the cat images I added to my project earlier. I only added 10 images so I reuse them. To use this code you should add 10 images to your  Images.xcassets and name them cat_0.jpg – cat_9.jpg.

If we were to run our app now we’d end up with something like this:

Schermafbeelding 2015-07-07 om 21.42.30

Not quite what we wanted.. but don’t worry, we’re going to implement our custom layout right now!

Step three: implementing the custom layout

Now that we’re all set up it’s time to get to business. First, create a now Cocoa Touch Class and call it “CustomCollectionViewLayout”. It should subclass  UICollectionViewFlowLayout. To avoid many small chunks of code I’ve grouped together some code in sensible groups, I’ll show you code first and then explain what it does right after that. Let’s get going with the first chunk:

This first section is responsible for the initial setup. It sets up some sizing values (remember that magic number 40 in our cell?) and it creates an array that we’ll use to store our layout in. When you’re creating a collection view that changes often or contains a lot of items you might not want to use this technique but since we have a relatively small collection that doesn’t change often we can cache our entire layout. There’s also a variable to hold the maxXPos , we’ll use that to calculate the collectionView’s content size later. In the  setup() function we configure the layout, these properties are inherited from the  UICollectionViewFlowLayout and allow us to set up spacings and a scrollDirection. In this case we’re not really using the spacings but I think it’s good practice to set them up anyway.

This piece of code comes after our initial setup, it overrides the prepareLayout  function which is called before the cells are actually going to need their layout. This allows us to pre-calculate our entire layout. Which is exactly what we want to do for this use case. There’s a loop inside this function that uses the  collectionView.numberOfItemsInSection function to find out how many items it is going to display. It then initializes layoutAttributes for the item at the current NSIndexPath and it calls  frameForItemAtIndexPath. To calculate the item’s frame. Next up is a check to determine of the x position for this item is the largest x position in our collection and then it stores the itemAttributes in our layout cache.

The  frameForItemAtIndexPath function uses the height of our collectionView to determine the amount of cells it can fit into a single column, then it determines how many rows there will be in our collection and based on that it calculates the x and y position for the item. Every other item will be offset somewhat to the right, we use the % operator and a ternary for that. If  currentRow % 2 == 0 the xPos is equal to  currentColumn*(itemWidth+self.minimumInteritemSpacing), otherwise it will be equal to  currentColumn*(itemWidth+self.minimumInteritemSpacing)+itemWidth*0.25. And finally we return a CGRect with the correct size and position values.

This last snippet of code actually provides our collection with the layout:

The first method,  layoutAttributesForItemAtIndexPath simply returns the layout attributes that belong to the passed IndexPath. Fairly straightforward. Next, we have  layoutAttributesForElementsInRect. This method is somewhat more complex because we get passed a  CGRect and we have to determine which items are inside of that area. To do this we loop over our layoutInfo object, we compare the rects and we return all intersecting items.

Finally, we calculate the collectionView’s contentSize. The contentWidth is equal to our  maxXPos + itemWidth and the height is the same as the collectionView’s height.

Step four: using the custom layout

The final step in this tutorial is to actually make the UICollectionView use our custom layout. To make this happen, select the Collection View Flow Layout object that is associated with your UICollectionView in your Main.storyboard and change it’s class to  CustomCollectionViewLayout.

Schermafbeelding 2015-07-07 om 22.14.33


Now build and run your app, you should see something like the image I showed you at the beginning of this post.


In conclusion

I hope this post is helpful to some of you out there. I had a lot of fun today figuring out how to do this myself and I figured there’s probably more people out there who are looking for cool ways to implement UICollectionView and use custom layouts.

The code for this project can be found on GitHub and if you want to reach out to me, I’m on Twitter.

Find every other element in an array with Swift

The other day somebody asked how they could retrieve every other element in an array using Swift. The solution they had tried was to use a for loop to go through all of the elements and then they would pop those elements off the array.  This seemed to work okay but only when all elements would be subsequent to each other. So an array like [0, 1, 2, 3, 4]  worked fine but when an array looked like  [90, 67, 45, 22, 123, 32] this approach didn’t work.

Luckily, swift has an enumerate function that allows you to loop through an array with both an index and the array value. The solution I eventually came up with was to enumerate the array and get the remainder from dividing the index by two in my loop. I then used that to determine if it was an even er odd index and then I printed the value of the element in the array. This might sound complex but the snippet is short and simple:

Simple enough, right? The enumerate function provides us with a way to loop through an array and get an index easily. That way we can write a clean for loop without doing something like var i = 0; i < array.count; i++ for example.

If you have questions about this you can send me a tweet and I’ll try to help. Happy Swifting!

My take on Protocols in Swift

When Apple announced Protocol extensions at this year’s WWDC and went on to explain the idea of Protocol Oriented Programming (video here), I think every iOS developer got really exited. Especially with Protocol extensions it seems that everything we will ever build can and will be protocol based instead of inheritance based like we do now with OOP. However, these extensions won’t be available until Swift 2.0 is released so we can’t use all of this new Protocol goodness yet. Or at least not all of it. This post is intended to get you up to speed with Protocols as they are in Swift 1.2 so you’ll be somewhat prepared once you can safely use Swift 2.0.

Taking advantage of Protocols today

To take advantage of the awesomeness of Protocols we could think of a Protocol as a mixin more than an interface. I’ve seen people compare Protocols to interfaces in, for instance, Java. While they are similar they will become quite different once we get to use protocol extensions.

If we can provide default implementations for our Protocol methods we should look at Protocol as little mixins of functionality that can be used to enhance existing types. Mixins are not exactly new in programming and if you look at functional programming mixins are considered pretty important. The cool thing about a mixin (or Protocol) driven approach is that it avoids complex, confusing and inflexible class hierarchies. Instead you can provide multiple Protocols, or mixins, to compile an object with. By doing this, the object will be very explicit about what it can and can’t do and the object type itself won’t matter throughout your code. What does matter throughout your code is the fact that an object contains certain functionality. And to make sure that an object has certain functionality it conforms to a protocol you wrote. Since this could be pretty confusing if you don’t use Protocol oriented programming yet, or if you’ve never heard of mixin based programming (or even Python’s multiple inheritance model), we should probably look at an example now.

An example

So let’s imagine that we’re mapping out some part of the animal kingdom, let’s start with an Animal class. This class will only contain the name of the animal and it’s size:

A subclass of animal will be Bird. A Bird will have an amount of legs and it will have a number of wings:

Now we’ll also create a Reptile class which will have a favoriteTemperature property so we know when the Reptile will be nice and comfortable.

A subclass of Reptile is a Crocodile, technically this is probably very incorrect, but that’s okay, in our imaginary animal kingdom anything goes. The Crocodile will get a number of legs property, just like the bird. It won’t get the wings though, flying crocodiles would be too scary for me.

As you might have noticed both Bird and Crocodile have a legs property. But if we were to create an application where somebody could pass any Animal they’d like and we’d try to make it walk we could do a check similar to this:

But this approach is prone to error because if we add a new animal with legs we will need to add a new section to our if statement to make sure that we allow that legged animal to walk. Not very developer friendly and basically a bug waiting to happen. We can do better than this by using protocols. Let’s refactor the Bird and Crocodile to implement a LeggedAnimal protocol:

All I did was define a protocol that forces implementers of that protocol to add a legs property to their object that can be get and set. That’s exactly what Bird and Crocodile already did so all we need to do is tell the outside world that we have implemented the LeggedAnimal protocol. Now we can also refactor the walk function:

Now that we have a protocol we can just make sure that anything we pass to the function is an implementer of the protocol we just wrote. Much cleaner and a lot less error prone. If we add new animals we just need to make sure that we make them comply with the LeggedAnimal protocol if we want them to be able to walk.

Wrapping up

In my own programs I only started making more use of protocols recently. I usually use them to make completely unrelated things relate to each other just like we did with the LeggedAnimal example. It’s a small protocols like this that allow for very flexible modeling and less worrying about subclasses and superclasses. Less inheritance usually means less unused code in classes and that’s a good thing.

The only downside at this moment is that you still have to provide an implementation of the required properties and methods. In swift 2.0 this will change because then you will be able to provide a default implementation via protocol extensions. These extensions will allow for even more flexible, DRY and powerful code. I’m looking forward to using those in my projects soon.

You can get the example code from this blogpost from my GitHub.

Icon fonts vs. svg icons

We can all agree that using png sprites for icons is not the most modern (or best) way to present icons on the web. Png is a rasterized format which means that if you try to make the image (or icon) larger, the quality will become worse. When browsers started properly supporting @font-face and svg some people chose to use icon fonts to serve their icons, others chose svg sprites to do this. These methods share the big benefit of scalability. This matters because our websites get viewed on many devices and you want your icons to be crisp on every device, not just the ones you optimized for by hand. This post is intended to give an overview of these two methods and to explore the benefits and drawbacks of each method. At the end of this post you will hopefully have an understanding of both svg icons and iconfonts and you’ll be able to choose one of these icon delivery methods for your own projects.

TL;DR: The comparison is very close, both have their big upsides and no real big downsides. I’d say iconfonts win because they’re a bit easier to use. Svg icons are a easier to position and manipulate. The code for this blogpost is on Github.

Getting set up


The first thing I’m going to compare is the set up process for each method. The method you end up choosing should not only work well but it should also be easy to manage. The first method I will set up is the iconfont. I will be using Gulp to automate the asset creation process. I made this decision because I use Gulp on all my projects. Also, Gulp seems like the right tool for this type of job; I don’t want to create my assets by hand. The icons I’m going to use were created by Jamison Wieser for The Noun Project.

Icon font

Like I mentioned, I will be using Gulp to generate my assets. The gulp-iconfont plugin seems like a good plugin to generate a font with. I also used the gulp-iconfont-css plugin so I didn’t have to create my own css template. With a couple of lines in my gulpfile and two plugins I managed to convert my svg icons into a font. Not bad!

svg icons

To make using the icons easy I will create a spritesheet that contains all my svg icons. I’ll be using gulp for this as well, just like I did for the iconfont. I’ve set up my output in “defs” mode. Which means that I can use the icons like Chris Coyier descrives in this post. This method only uses one gulp plugin but the fact that this gulp plugin uses svg-sprite which has a ton of options, it does seem a little less straightforward to set up. The output that was produced seems decent on first viewing so that’s good.

Easiest to set up

Both methods are actually easy to set up within about 5-10 minutes. Therefor, this section will be a tie. Both methods are easy to set up and there isn’t a clear winner.


Something we should always take into consideration is the file size of the things we end up using. So, a simple comparison in filesize:

iconfont: 8kb (or 12kb if the svg font is used)
spritesheet: 25kb

Best filesize

The winner in this example is the iconfont. The iconfont is significantly less Kb than the spritesheet is.

Ease of use

Whenever I pick a technique I want to use, it has to be something that’s easy to use. Of course it’s important that something works well, is fast and lightweight and more but I feel like ease of use should be mentioned right alongside those requirements because in the end you might end up working with the tool or technique you chose for quite some time. So for my own sanity, I like something that’s easy to use.


To implement the iconfont all you have to do is add the stylesheet to the  head  of your document. In order to use the icons you just create span  elements and give them the icon class. The second class you give them is your icon’s name. An example:

Easy enough, right? This results in the following rendered output:

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To implement the svg spritesheet I needed a polyfill to make everything work. That’s because IE doesn’t support the <use> method for external svgs and I didn’t want to include the whole svg inside of my html body. For more info refer to this post. The html I ended up using looks like this:

This is quite a bit more complicated than the iconfont method. I had to figure out the proper viewBox settings for my icon and I have to do a lot more typing.


When you want to position your icon with the iconfont method you’ll run into some weird and complicated stuff eventually. That’s because the iconfont is rendered as text so for example, there’s line-height applied to it. This could lead to unpredictable and strange behavior in some cases.

When you use the spritesheet approach you get to decide almost everything. The sizing, positioning, display style, you can all directly manipulate it as if you’re manipulating an image. So for positioning, the spritesheet is definitely better.


When you want to style your icons you’re going to love the spritesheet approach. because you’re working with actual svg icons you can set strokes, fill colors and everything. Just like you might do with any other svg! The iconfont however is flattened in a way. You can set a color for the whole icon bt you can’t style individual sections, so the spritesheet is more customizable than the iconfont is.

The easiest to use method

Even though it’s a little bit more work to implement, the spritesheet wins. It’s easier to position and the more powerful styling options are also a big advantage over an iconfont. So the winner for this section is spritesheet, hands down.

Render quality

Personally I haven’t seen the difference yet but there are definitely some potential rendering differences between the spritesheet and an iconfont. Because an iconfont is rendered by the browser as a font, it is also anti aliased. The result of this could be that your icons look less sharp if they’re used as a font. Like I said, I haven’t had any issues with this in the real world but the potential is there.

The best rendering method

Even though the rendering seems to be nearly identical the spritesheet wins here. That’s because an iconfont can potentially suffer from a lack of sharpness due to anti aliasing of the browser.

Browser support

The  @font-face method of embedding custom fonts is supported by all major browsers so it’s very safe to use. The spritesheet method is supported by all browsers except for IE. However, a polyfill called svg4everybody is available so at the end of the day both methods are available on all major browsers.

The best browser support

Because the spritesheet method requires a polyfill and the iconfont doesn’t I declare the iconfont the winner of the browser support section.

And the winner is..

After exploring and comparing both the iconfont and spritesheet approach I can honestly say that the comparison is very close. The iconfont is better at the implementation, more lightweight and it has better browser support. The spritesheet is more flexible, easier to work with and has great browser support if you include a polyfill.

Earlier in the article I mentioned that one of the major factors for me to decide on things like this is ease of use. And because of that I would say that the iconfont wins. The decision is really tough actually because I’m not a fan of how you have to mess around in order to position an icon with this technique. Nor am I a fan of the anti aliasing risks because I like my icons to be sharp and crisp. But iconfonts are lightweight, easy to use and implement in general and I’ve never come across a situation where I actually had to style parts of an icon rather than change the color of the entire icon. So, yeah, that concludes this post. Iconfonts win. If you beg to differ or have feedback for me, please send me a Tweet. I’d love to your opinions on this.

If you want to have a look at the source files I’ve used, the repo is on located right here on Github.

How to choose between rem and em

A few days ago I found this article that argues for using rem units when defining font sizes. Generally speaking this is good advice. The rem comes with great predictable behavior, just like pixels do. But the rem also comes with accessibility advantages. When a user changes the font size in their browser settings, the rem and em unit will both respect that and resize accordingly while the pixel unit doesn’t. That’s great news for the user. But how do you choose between rem or em? Time to go in depth on what these units do. First I’ll explain how each unit works and what they do. Based on that I’ll explain how you can make the decision for a sizing unit.

The rem unit

Since the rem unit is the easiest one to understand and use, it will be the sizing unit I start off with. The rem is relatively new but if you don’t have to support IE8 anymore you can safely use it. Rem is short for “root em”, that’s because it is a lot like the em unit except it is relative to the root font size.

So, what does this all mean? The rem unit is a sizing unit that’s related to font size. With default browser settings 1 rem should be equal to 16px. That is because the default browser font size is, you may have guessed it, 16px. So using rems is almost as easy as using pixels. Want to make something 80px wide? That will be 5 rem please.

More complicated things like 100px will require you to do some math but if you use something like Sass I recommend that you check out, it provides a rem-calc function to help you calculate rems.

A workaround many people use is to set the body’s main font-size to 10px so 1 rem equals 10px on their website instead of 16px which will make working with rems a lot easier. The cool thing about the rem unit is the fact that 1 rem will always be the same size everywhere on the page, no matter what.

The em unit

The em unit is a lot like the rem unit. The difference between them is that the rem unit is always relative the the root font size. The em unit is relative to it’s containing element. An h1 that is directly inside of the body and has a font size of 2 em will have a font size of 32px if we assume the default browser font size is in tact. If you would add a link inside of that h1 and you would want that to be 24px you first instinct would probably be to use 1.5 em as a font-size for that anchor tag. Let’s try this out.

So… what went wrong here? The header has a 2 em font size, the anchor is 1.5 em so the anchor should be smaller that the rest of the text, right? Except, the anchor is larger than the rest of the header text which makes no sense. Remember that I stated earlier that the em unit is relative to it’s containing element? That’s why the anchor is larger than the header text. The anchor is a child of the header so a 1.5 em font-size means that the anchor’s font size should be 1.5 times the size of the anchor text.

This is something that makes the em a complicated unit to work with, you can imagine that deep nesting with multiple font sizes can get really ugly at some point. A simple demonstration:

What you see here is a list with a nested list. The outer list has a larger font size than the inner list. This happened because I set a 0.8 em font size on the ul tag. So when there’s a nested list, this 0.8 em is relative to the 0.8 em font size the outer list already has. So the outer list is 80% the font size of the body. The nested list is 80% the font size of the outer list. Confused? I understand, the em isn’t a very straightforward unit.

Making the decision

Now that we know how both units work we should be able to make an informed decision. So, should we use rem or do we use em for our sizing? The answer, according to me, should be both. Whenever you want to have absolute control over a size you probably want to use rem. An example would be an element that you would normally make 100px wide. You want that element to have the same size, no matter where in the document you use it, the size has to be 100px. That is a case where you should convert that 100px to rems.

However, there are cases like the link inside of an header element where you might not want to set an absolute size. You might want to say this header element should have a font size that is two times larger than the body text that it’s above. That would mean that you want to use a 2 em font size because then you know that your header is always two times larger than the body text of the element. Taking this one step further you might want to say that the anchor tag’s font size should be 75% percent of the header’s font size. That’s 0.75 em.

What I would like to conclude here is that both of these sizing units are extremely powerful. One is very good for setting absolute sizes that are still accessible and adaptable. The other is good for setting relative sizes, whenever something should be x times the size of something else, regardless how big, the em unit is your friend. I do think, however that the rem units should be the unit of choice in many situations. But especially with margins, paddings and certain spacing situations I have found the em unit to be the best choice because all those sizes are usually relative to another size and that’s where the em shines bright.

So, next time you’re faced with the rem vs. em decision I hope you think about the way they each work and make an informed decision. My rule of thumb is: rem replaces absolute pixel sizes, em is for relative sizes. If you have questions for me, feedback or want to get in touch you can always contact me on Twitter.

Consistency and discipline over motivation

One of the beautiful things about being a developer is that many of us actually have the opportunity to take an activity we enjoy, and make it our job. Many developers are happy to do some extra work or learn something when they’re at home or in the weekend just because they are so eager to learn and play. While this is pretty awesome, it won’t last forever. You won’t be motivated to learn every single day. Especially once you start doing development as a full-time job. I experience this as well, sometimes I have a couple of days or even weeks where my motivation is through the roof. I’ll get tons of work done and the days just fly by. On other days I just can’t seem to get started, everything is distracting and the motivation just doesn’t seem to be there. When I look at some of the more senior developers I know, it seems that they have moved past this phase. They always seem to be motivated and sometimes they just seem extra motivated. They just seem to have no shortage of the good stuff! How do they do this?

Is it motivation you should look for?

If you think about it, motivation isn’t worth much. It’s just not there all the time and you can’t build a solid career based on it. When I was looking for ways to improve motivation I came across posts like this, telling me that I should get disciplined. Some went even further and said that motivation just isn’t worth your time.

Because of these posts I started to realize that motivation is a great driver of productivity. But only when it’s there. When motivation isn’t there, every job seems like a chore. Have to adjust a form on a website? It sounds terrible when you’re not motivated. You’d have to create a new input field, maybe change a database table and more. You get tired just by thinking about it. But then consider doing that same thing when you’re motivated. You probably would get excited because you get to possibly improve the product and code base that you’re working on. This isn’t feasible in the long run though, when you want a job in development you’ll need to train yourself to become more consistent, more disciplined. Motivation will be the bonus, not the requirement.

Changing motivation into discipline

If you want to be more disciplined you’ll sometimes have to be pretty tough on yourself. There’s rarely a valid excuse to not do what you’re supposed to do. So instead of postponing things until you feel motivated or obliged to do them, just get started. If you do this, and are consistent about it, you’ll see that it helps. I often find that it helps to not jump in headfirst like you would when you’re super motivated but to just sit back first. Take 15-20 minutes to figure out what it is that you’re going to build, what code are you going to write. Figure out what sub tasks there are and split them up in blocks that will take about 40 minutes to complete. If you do this, you will have a great structured overview of what you’re going to do. You’ll know how busy you are for the day or week and you’ll be able to plan accordingly. During those 40 minute work cycles try to turn off notifications that might distract you. Discipline yourself to only check notifications in between your 40 minute cycles.

After a 40 minute cycle it’s time to take a quick break. And try to make it an actual break, get up and grab a drink. If there’s email or anything similar that requires your attention, take a peek. Reply if needed or add replying to your to-do list. Make it a part of a 40 minute cycle if the email requires you to figure something out in-depth. Otherwise, use the break or extend the break a little (but not too much, 10 minutes should be the maximum). In the beginning you might feel like you’re restricting yourself because everything has to be thought about or planned in, you can’t just start doing something and then do something else until you’re out of motivation. That’s fine, you are training yourself to have a consistent and disciplined workflow. If you find that 40 minutes is too long or too short for you you can always change the cycles. You could even do that on a day-to-day basis if you feel like it’s appropriate for the tasks you’re working on. I personally found after a few weeks that I prefer 50 minute cycles with 10-15 minute breaks.

The benefits are real

When I look at more senior developers I notice that many of them have a workflow similar to this. They take multiple short breaks throughout the day and between those breaks they tend to be very focused on the tasks they have to complete. They don’t have their Slack open all the time and they work on a single thing at a time. And they are consistent about that. Everyday they seem to be able to flick the switch and go into work mode. Of course they still have more and less motivated days, but a motivated day will just make them super productive instead of only productive because being productive is their default setting.

So let’s get out there and become consistently more disciplined!

Using Flexbox in the real world

The Flexbox module for css was built with the intent to make a more robust, less hacky way to layout elements on pages. When you’re building a webpage you often don’t know how high or wide every element could or should be. This can cause problems in certain layouts which lead to ugly hacks. Flexbox solves this widespread layout issue. The module has been in development for quite some time and the W3C gave the spec a “last call working draft” status back in september of 2014. The browser support for this module is very good if you don’t have to support IE9 so you can safely use it. In this post I will provide a few code examples to show you how you can use Flexbox in some everyday situations.

Creating a filmstrip

Have you ever created a horizontally scrolling filmstrip kind of module? You know the size of the each element in the strip and the size of the containing element but the size of the inner element, the filmstrip itself is unknown. This would normally result in a layout like this and you would have to use Javascript or hardcode the size of the inner element to make this work.

So what would happen if you used Flexbox for this? Well, Flexbox allows an element to grow, not only on the y axis like an element normally does, but also on the x axis. It’s one of the reasons Flexbox is really cool. Let’s try this.

It’s pretty neat, isn’t it? Between the first and second example there’s only three lines of code that are different. Okay, actually there’s a little more but I’m not counting in the vendor prefixes because you don’t have to write those if you use an autoprefixer. The first difference is that we give  overflow-x: scroll; to the filmstrip container, that’s just to make the contents scroll. The second step is to set  display: flex; on the inner element. If you did only these two things, the items inside of the inner element will shrink to fit inside of their container. You don’t want this so the last thing you do is add  flex-shrink: 0; to the filmstip items. The shrink property has a value of 0(false) or 1(true). There’s also a  flex-grow  property, it’s the same as the shrink property but it determines whether an element will grow or not.

Vertical centering

Ever since I started writing css this has been a problem. How do you center an element, with or without a known height, in a container that is or isn’t flexible? No matter how you look at it, vertical centering is annoying. I’ve used hacks that would absolutely position the centered element at 50% from the top and then I would use a negative top margin to push the element towards the center. Another method is to use translating which is slightly cleaner but you still have to use position absolute and a top offset of 50%. You could display your stuff as if it’s a table and then vertically center content which works well but it just doesn’t feel right. It starts to feel plain wrong once you’ve tried to do this with Flexbox.

So in this example I’ve set up a container and inside of that container is an image. Flexbox is used to center the image both vertically and horizontally inside of it’s containing element. The property that is used for vertical centering is  align-items . The property that is centering horizontally in this example is  justify-content . In my opinion, this is the best way to vertically align items I’ve seen.

Fitting things into a container

The filmstrip example gave this one away already but Flexbox can be used to fit an unknown number of items into a container. This is really nice if you have a couple of images but you can’t really be sure of how many. You could optimize for a certain number, let’s say four in the case of this example. And then for the edge cases where you have five images or more, you have Flexbox to make the images smaller so everything will still fit nicely into the containing element. Let’s check it out.

All we had to do to achieve this is add  display: flex; to the containing element. In the first example we saw that, by default, children of an element with  display: flex; will shrink to fit inside of that container.

Conclusions and further resources

In this post I showed you three examples of what you can achieve with Flexbox and how you can do that. Note that we just used Flexbox for three small things and that I didn’t mention Flexbox as a method of laying out your entire page. The reason for this is that Flexbox is not intended for that. There is a spec on the way for laying out your entire page and it’s called grid.

If you’re looking for a good overview of how Flexbox works I recommend that you visit this cheatsheet on This cheatsheet provides a lot of information on how you can use Flexbox and what properties it has. Lastly, if you’re looking for more examples of what problems you can solve with Flexbox check out this “solved by Flexbox” page.

Service workers are awesome

In the war between native and web apps there’s a few aspects that make a native app superior to a web app. Among these are features like push notifications and offline caching. A native app, once installed, is capable of providing the user with a cache of older content (possibly updated in the background) while it’s fetching new, fresh content. This is a great way to avoid loading times for content and it’s something that browser vendors tried to solve with cache manifests and AppCache. Everybody who has tried to implement offline caching for their webpages will know that the AppCache manifest files are a nightmare to maintain and that they’re pretty mysterious about how and when they store things. And so the gap between native and web remained unchanged.

In comes the service worker

The service worker aims to solve all of our issues with this native vs. web gap. The service worker will allow us to have a very granular controlled cache, which is great. It will also allow us to send push notifications, receive background updates and at the end of this talk Jake Archibald mentions that the Chrome team is even working on providing stuff like geofencing through the service worker API. This leads me to think that the service worker just might become the glue between the browser and the native platform that we might need to close the gap once and for all.

If you watch the talk by Jake Archibald you’ll see that the service worker can help a great deal with speeding up page loads. You’ll be able to serve cached content to your users first and then add new content later on. You’re able to control the caching of images that aren’t even on your own servers. And more importantly, this method of caching is superior to browser caching because it will allow for true offline access and you can control the cache yourself. This means that the browser won’t just delete your cached data whenever it feels the need to do so.

How the service worker works

When you want to use a service worker you have to install it first. You can do this by calling the register function on  navigator.serviceWorker . This will attempt to install the service worker for your page. This is usually the moment where you’ll want to cache some static assets. If this succeeds the service worker is installed. If this fails the service worker will attempt another install the next time the page is loaded, your page won’t be messed up if the installation fails.

Once the service worker is installed you can tap into network requests and respond with cached resources before the browser goes to the network. For example, the browser wants to request /static/style.css . The service worker will be notified through the  fetch event and you can either respond with a cached resource or allow the browser to go out and fetch the resource.

HTTPS only!!

Because the server worker is such a powerful API it will only be available through HTTPS when you use it in production. When you’re on localhost HTTP will do but otherwise you are required to use HTTPS. This is to prevents man-in-the-middle attacks. Also, when you’re developing locally you can’t use the file:// protocol, you will have to set up a local webserver. If you’re struggling with that, I wrote this post that illustrated three ways to quickly set up an HTTP server on your local machine. When you want to publish a demo you can use github pages, these are server over HTTPS by default so service workers will work there.

A basic server worker example

Browser support

Before I start with the example I want to mention that currently Chrome is the only browser that supports service workers. I believe Firefox is working hard to make an implementation happen as well and the other vendors are vague about supporting the service worker for now. This page has a good overview of how far the completion of service workers is.

The example

The best way to illustrate the powers of the service worker probably is to set up a quick demo. We’re going to create a page that has ten pretty huge pictures on it, these pictures will be loaded from several resources because I just typed ‘space’ in to Google and picked a bunch of images there that I wanted to include on a webpage.

When I load this page without a service worker all the images will be fetched from the server, which can be pretty slow considering that we’re using giant space images. Let’s speeds things up. First create an app.js  file and include that in your page html right before the body tag closes. In that file you’ll need the following script:

This code snipper registers a service worker for our website. The register function returns a promise and when it gets resolved we just log the words ‘success’ for now. On error we’ll log failure. Now let’s set up the service worker.

The code above creates a new service worker that adds a list of files to the  "SPACE_CACHE" . The install eventHandler will wait for this operation to complete before it returns a success status, so if this fails the installation will fail as well.

Now let’s write the fetch handler so we can respond with our freshly cached resources.

This handler will take a request and match it against the SPACE_CACHE. When it finds a valid response, it will respond with it. Otherwise we will use the fetch API that is available in service workers to load the request and we respond with that. This example is pretty straightforward and probably a lot more simple than what you might use in the real world.


Debugging service workers is far from ideal, but it’s doable. In Chrome you can load chrome://serviceworker-internals/ or chrome://inspect/#service-workers to gain some insights on what is going on with your service workers. However, the Chrome team can still improve a lot when it comes to debugging service workers. When they fail to install properly because you’re not using the cache polyfill for instance, the worker will return a successful installation after which the worker will be terminated without any error messages. This is very confusing and caused me quite a headache when I was first trying service workers.

Moving further with service workers

If you think service workers are interesting I suggest that you check out some examples and posts online. Jake Archibald wrote the <a href=”” target=”_blank”>offline cookbook</a>. There’s many information on service workers in there. You can also check out his <a href=”” target=”_blank”>simple-serviceworker-tutorial</a> on Github, I learned a lot from that.

In the near future the Chrome team will be adding things like push notifications and geofencing to service workers so I think it’s worth the effort to have a look at them right now because that will really put you in the lead when service workers hit the mainstream of developers and projects.

If you feel like I made some terrible mistakes in my overview of service workers or if you have something to tell me about them, please go ahead and hit me up on Twitter.

The source code for this blog post can be found on Github.