How to use modifiers on modifiers with BEM?

• about 3 minutes reading

For the last few project I’ve had the pleasure of naming my SCSS-files with the BEM methodology. The upside is easier maintainable files and far more informative class-names.

The BEM syntax is very strict and the naming convention follows this pattern:

.block {}
.block__element {}
.block--modifier {}

If you haven’t used BEM or haven’t got your head around BEM yet I highly recommend this article by Harry Roberts.

Usually it’s rather easy to tell if you are making a block, an element or a modifier, but one problem I’ve had again and again is a modifier on a modifier. Take this example:

We have these two buttons called .button--primary and .button--secondary coded like this:

<a href="#" class="button button--primary">Main attention</a>
<a href="#" class="button button--secondary">Cancel</a>

..and looking like this:

How the buttons looks normally

This works great on the regular background, but as you can see we got a problem if we need to wrap the buttons in a red warning-box or similar. We still want the same look, but maybe not green on red?

How the buttons looks on a red background

A few solutions comes to mind:

  1. .button--secondary--inverted

    We could add a modifier to .button--secondary. This just overrides the values that we need to change and we still need to add .button--secondary to the button. This feels a bit wrong and is very tiresome to write out. The code is however very logic to read and builds nicely on the BEM syntax.

  2. .button--secondary-inverted

    We make a seperate modifier which is almost a duplicate of .button--secondary, just changing the colors that we need to change. This is also very nice to read, but feels very bloated since you are copying almost every style.

  3. .button--inverted

    We create a .button--inverted class that changes .button--primary and .button--secondary if they have the .button--inverted class. Ex:

    .button--inverted {
&.button--primary {
color: black;
background-color: white;
}
&.button--secondary {
color: white;
border-color: white;
}
}

    This solution is a bit inconsistent with the BEM naming since we are using nesting. However the HTML is very nice to read and easy to remember. It also means that we can easily toggle the .button--inverted class with javascript without having to worry about if this class later on is going to be a .button--primary or a .button--secondary – the invertion will still work.

  4. .box--notification .button--secondary

    We could also nest the styling and say if .button--secondary is inside .box--notification we always want it to be white. This is probably the most dirty way to do it, but why not when you never want a green button inside a red box? The downside here is reusability and the location of the code. The big upside of BEM is the structure and that we from the name know the location of every class. If we suddenly start to nest classes we miss control.

I’m still not sure what is the best solution here. For now I’ve landed on alternative 3 mainly because the simplicity and readability. I’m eager to hear your thoughts and ideas. Give me a word on twitter or on mail about your thoughts.

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