author: Krasimir Tsonev

Krasimir is a blogger, who writes and speaks.
He loves open source and codes awesome stuff.

SASS: universal mixin for box model properties

I'm currently working on OrganicCSS - a micro framework based on atomic CSS concept. I'm thinking a lot for name conventions, classes and of course mixins. I decided to combine three mixins in a file called _box-model.scss. They will provide a shortcuts for margin, padding and border properties.

That's what I start from:

@mixin margin($values...) {
    margin: $values;
}
@mixin padding($values...) {
    padding: $values;
}
@mixin border($values...) {
    border: $values;
}

I could say that for margin and padding such kind of mixin is good enough. However the border once is not flexible at all. That's because very often I set only border-top property. So, instead of that I decided to pass four parameters and transform the code to

@mixin border($top, $right, $bottom, $left) {
    border-top: $top;
    border-right: $right;
    border-bottom: $bottom;
    border-left: $left;
}

But now it requires four arguments to be passed. That's not good, because I'll have to write more, which is exactly the opposite of what I was trying to achieve. Thankfully SASS offers default values for the mixin's parameters and this helps a lot.

@mixin border($top: none, $right: none, $bottom: none, $left: none) {
    border-top: $top;
    border-right: $right;
    border-bottom: $bottom;
    border-left: $left;
}

So, the mixin changes several times and I simply wrote a short list of requirements, which I wanted to accomplish:

  • should accept no arguments
  • should reset the property
  • should support applying value to only certain versions of the property (i.e. border-left, border-right etc ...)
  • it should be possible to pass only one parameter and apply it to all the versions sides

A good check list, isn't it. The first one could be covered if I define default values for all the arguments. The second one is also doable if the defaults are properly set. And the fact that I have predefined values means that I'm able to send only the last property, so the third point could be also marked as done. The last one is a little bit tricky and require the usage of @if directive. Here is the final version:

@mixin border($top: none, $right: none, $bottom: none, $left: none) {
    border-top: $top;
    @if $right == none {
        border-right: $top;
    } @else {
        border-right: $right;
    }
    @if $bottom == none {
        border-bottom: $top;
    } @else {
        border-bottom: $bottom;
    }
    @if $left == none {
        border-left: $top;
    } @else {
        border-left: $left;
    }
}

I used the same concept for padding and margin mixins.


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