Creating or referencing variables dynamically in Sass

Solution 1:

This is actually possible to do using SASS maps instead of variables. Here is a quick example:

Referencing dynamically:

$colors: (
  blue: #007dc6,
  blue-hover: #3da1e0
);

@mixin colorSet($colorName) {
    color: map-get($colors, $colorName);
    &:hover {
        color: map-get($colors, #{$colorName}-hover);
    }
}
a {
    @include colorSet(blue);
}

Outputs as:

a { color:#007dc6 }
a:hover { color:#3da1e0 }

Creating dynamically:

@function addColorSet($colorName, $colorValue, $colorHoverValue: null) {
  $colorHoverValue: if($colorHoverValue == null, darken( $colorValue, 10% ), $colorHoverValue);

  $colors: map-merge($colors, (
    $colorName: $colorValue,
    #{$colorName}-hover: $colorHoverValue
  ));

  @return $colors;
}

@each $color in blue, red {
  @if not map-has-key($colors, $color) {
    $colors: addColorSet($color, $color);
  }
  a {
    &.#{$color} { @include colorSet($color); }
  }
}

Outputs as:

a.blue { color: #007dc6; }
a.blue:hover { color: #3da1e0; }
a.red { color: red; }
a.red:hover { color: #cc0000; }

Solution 2:

Sass does not allow variables to be created or accessed dynamically. However, you can use lists for similar behavior.

scss:

$list: 20px 30px 40px;    
@mixin get-from-list($index) {
  width: nth($list, $index);
}

$item-number: 2;
#smth {
  @include get-from-list($item-number);
}

css generated:

#smth {
  width: 30px; 
}

• http://sass-lang.com/docs/yardoc/file.SASS_REFERENCE.html#lists
• http://sass-lang.com/docs/yardoc/Sass/Script/Functions.html#list-functions

Solution 3:

Anytime I need to use a conditional value, I lean on functions. Here's a simple example.

$foo: 2em;
$bar: 1.5em;

@function foo-or-bar($value) {
  @if $value == "foo" {
    @return $foo;
  }
  @else {
    @return $bar;
  }
}

@mixin do-this($thing) {
  width: foo-or-bar($thing);
}

Solution 4:

Here's another option if you're working with rails, and possibly under other circumstances.

If you add .erb to the end of the file extension, Rails will process erb on the file before sending it to the SASS interpreter. This gives you a can chance to do what you want in Ruby.

For example: (File: foo.css.scss.erb)

// Set up variable and mixin
$foo-baz: 20px; // variable

<%
def do_this(bar)
  "width: $foo-#{bar};"
end
%>

#target {
  <%= do_this('baz') %>
}

Results in the following scss:

// Set up variable and mixin
$foo-baz: 20px; // variable

#target {
  width: $foo-baz;
}

Which, of coarse, results in the following css:

#target {
  width: 20px;
}

Solution 5:

I came across the need to reference a colour dynamically recently.

I have a _colours.scss file for every project, where I define all my colours once and reference them as variables throughout.

In my _forms.scss file I wanted to setup button styles for each colour available. Usually a tedious task. This helped me to avoid having to write the same code for each different colour.

The only downside is that you have to list each colour name and value prior to writing the actual css.

// $red, $blue - variables defined in _colours.scss
$colours: 
  'red' $red,
  'blue' $blue;

@each $name, $colour in $colours {
  .button.has-#{$name}-background-color:hover {
    background-color: lighten($colour, 15%);
  }
}