Lists

Compatibility (Square Brackets):
Dart Sass
LibSass
since 3.5.0
Ruby Sass
since 3.5.0

Older implementations of LibSass and Ruby Sass didn’t support lists with square brackets.

Lists contain a sequence of other values. In Sass, elements in lists can be separated by commas (Helvetica, Arial, sans-serif) or by spaces (10px 15px 0 0), as long as it’s consistent within the list. Unlike most other languages, lists in Sass don’t require special brackets; any expressions separated with spaces or commas count as a list. However, you’re allowed to write lists with square brackets ([line1 line2]), which is useful when using grid-template-columns.

Sass lists can contain one or even zero elements. A single-element list can be written either (<expression>,) or [<expression>], and a zero-element list can be written either () or []. Also, all list functions will treat individual values that aren’t in lists as though they’re lists containing that value, which means you rarely need to explicitly create single-element lists.

Using Lists

Sass provides a handful of functions that make it possible to use lists to write powerful style libraries, or to make your app’s stylesheet cleaner and more maintainable.

Indexes

Many of these functions take or return numbers, called indexes, that refer to the elements in a list. The index 1 indicates the first element of the list. Note that this is different than many programming languages where indexes start at 0! Sass also makes it easy to refer to the end of a list. The index -1 refers to the last element in a list, -2 refers to the second-to-last, and so on.

Access an Element

Lists aren’t much use if you can’t get values out of them. You can use the nth($list, $n) function to get the element at a given index in a list. The first argument is the list itself, and the second is the index of the value you want to get out.

SCSS Syntax

@debug nth(10px 12px 16px, 2); // 12px
@debug nth([line1, line2, line3], -1); // line3

Sass Syntax

@debug nth(10px 12px 16px, 2)  // 12px
@debug nth([line1, line2, line3], -1)  // line3

Do Something for Every Element

This doesn’t actually use a function, but it’s still one of the most common ways to use lists. The @each rule evaluates a block of styles for each element in a list, and assigns that element to a variable.

SCSS Syntax

$sizes: 40px, 50px, 80px;

@each $size in $sizes {
  .icon-#{$size} {
    font-size: $size;
    height: $size;
    width: $size;
  }
}








Sass Syntax

$sizes: 40px, 50px, 80px

@each $size in $sizes
  .icon-#{$size}
    font-size: $size
    height: $size
    width: $size










CSS Output

.icon-40px {
  font-size: 40px;
  height: 40px;
  width: 40px;
}

.icon-50px {
  font-size: 50px;
  height: 50px;
  width: 50px;
}

.icon-80px {
  font-size: 80px;
  height: 80px;
  width: 80px;
}

Add to a List

It’s also useful to add elements to a list. The append($list, $val) function takes a list and a value, and returns a copy of the list with the value added to the end. Note that because Sass lists are immutable, it doesn’t modify the original list.

SCSS Syntax

@debug append(10px 12px 16px, 25px); // 10px 12px 16px 25px
@debug append([col1-line1], col1-line2); // [col1-line1, col1-line2]

Sass Syntax

@debug append(10px 12px 16px, 25px)  // 10px 12px 16px 25px
@debug append([col1-line1], col1-line2)  // [col1-line1, col1-line2]

Find an Element in a List

If you need to check if an element is in a list or figure out what index it’s at, use the index($list, $value) function. This takes a list and a value to locate in that list, and returns the index of that value.

SCSS Syntax

@debug index(1px solid red, 1px); // 1
@debug index(1px solid red, solid); // 2
@debug index(1px solid red, dashed); // null

Sass Syntax

@debug index(1px solid red, 1px)  // 1
@debug index(1px solid red, solid)  // 2
@debug index(1px solid red, dashed)  // null

If the value isn’t in the list at all, index() returns null. Because null is falsey, you can use index() with @if or if() to check whether a list does or doesn’t contain a given value.

SCSS Syntax

$valid-sides: top, bottom, left, right;

@mixin attach($side) {
  @if not index($valid-sides, $side) {
    @error "#{$side} is not a valid side. Expected one of #{$sides}.";
  }

  // ...
}

Sass Syntax

$valid-sides: top, bottom, left, right

@mixin attach($side)
  @if not index($valid-sides, $side)
    @error "#{$side} is not a valid side. Expected one of #{$sides}."


  // ...

Immutability

Lists in Sass are immutable, which means that the contents of a list value never changes. Sass’s list functions all return new lists rather than modifying the originals. Immutability helps avoid lots of sneaky bugs that can creep in when the same list is shared across different parts of the stylesheet.

You can still update your state over time by assigning new lists to the same variable, though. This is often used in functions and mixins to collect a bunch of values into one list.

SCSS Syntax

$prefixes-by-browser: ("firefox": moz, "safari": webkit, "ie": ms);

@function prefixes-for-browsers($browsers) {
  $prefixes: ();
  @each $browser in $browsers {
    $prefixes: append($prefixes, map-get($prefixes-by-browser, $browser));
  }
  @return $prefixes;
}

@debug prefixes-for-browsers("firefox" "ie"); // moz ms

Sass Syntax

$prefixes-by-browser: ("firefox": moz, "safari": webkit, "ie": ms)

@function prefixes-for-browsers($browsers)
  $prefixes: ()
  @each $browser in $browsers
    $prefixes: append($prefixes, map-get($prefixes-by-browser, $browser))

  @return $prefixes


@debug prefixes-for-browsers("firefox" "ie")  // moz ms

Argument Lists

When you declare a mixin or function that takes arbitrary arguments, the value you get is a special list known as an argument list. It acts just like a list that contains all the arguments passed to the mixin or function, with one extra feature: if the user passed keyword arguments, they can be accessed as a map by passing the argument list to the keywords() function.

SCSS Syntax

@mixin syntax-colors($args...) {
  @debug keywords($args); // (string: #080, comment: #800, $variable: $60b)

  @each $name, $color in keywords($args) {
    pre span.stx-#{$name} {
      color: $color;
    }
  }
}

@include syntax-colors(
  $string: #080,
  $comment: #800,
  $variable: #60b,
)

Sass Syntax

@mixin syntax-colors($args...)
  @debug keywords($args)  // (string: #080, comment: #800, $variable: $60b)

  @each $name, $color in keywords($args)
    pre span.stx-#{$name}
      color: $color




@include syntax-colors($string: #080, $comment: #800, $variable: #60b);




CSS Output

pre span.stx-string {
  color: #080;
}

pre span.stx-comment {
  color: #800;
}

pre span.stx-variable {
  color: #60b;
}