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152 lines
4.8 KiB
Plaintext
152 lines
4.8 KiB
Plaintext
---
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title: Interpolation
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table_of_contents: true
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introduction: >
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Interpolation can be used almost anywhere in a Sass stylesheet to embed the
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result of a [SassScript expression](syntax/structure#expressions) into a chunk
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of CSS. Just wrap an expression in `#{}` in any of the following places:
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---
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* [Selectors in style rules](style-rules#interpolation)
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* [Property names in declarations](style-rules/declarations#interpolation)
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* [Custom property values](style-rules/declarations#custom-properties)
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* [CSS at-rules](at-rules/css)
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* [`@extend`s](at-rules/extend)
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* [Plain CSS `@import`s](at-rules/import#plain-css-imports)
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* [Quoted or unquoted strings](values/strings)
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* [Special functions](syntax/special-functions)
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* [Plain CSS function names](at-rules/function#plain-css-functions)
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* [Loud comments](syntax/comments)
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<% example do %>
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@mixin corner-icon($name, $top-or-bottom, $left-or-right) {
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.icon-#{$name} {
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background-image: url("/icons/#{$name}.svg");
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position: absolute;
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#{$top-or-bottom}: 0;
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#{$left-or-right}: 0;
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}
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}
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@include corner-icon("mail", top, left);
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===
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@mixin corner-icon($name, $top-or-bottom, $left-or-right)
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.icon-#{$name}
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background-image: url("/icons/#{$name}.svg")
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position: absolute
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#{$top-or-bottom}: 0
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#{$left-or-right}: 0
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@include corner-icon("mail", top, right)
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<% end %>
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## In SassScript
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<% impl_status dart: true, libsass: false, ruby: '4.0.0 (unreleased)', feature: "Modern Syntax" do %>
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LibSass and Ruby Sass currently use an older syntax for parsing interpolation
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in SassScript. For most practical purposes it works the same, but it can
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behave strangely around [operators][]. See [this document][] for details.
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[operators]: operators
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[this document]: https://github.com/sass/language/blob/master/accepted/free-interpolation.md#old-interpolation-rules
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<% end %>
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Interpolation can be used in SassScript to inject SassScript into [unquoted
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strings][]. This is particularly useful when dynamically generating names (for
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example for animations), or when using [slash-separated values][]. Note that
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interpolation in SassScript always returns an unquoted string.
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[unquoted strings]: values/strings#unquoted
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[slash-separated values]: operators/numeric#slash-separated-values
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<% example do %>
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@mixin inline-animation($duration) {
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$name: inline-#{unique-id()};
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@keyframes #{$name} {
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@content;
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}
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animation-name: $name;
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animation-duration: $duration;
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animation-iteration-count: infinite;
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}
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.pulse {
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@include inline-animation(2s) {
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from { background-color: yellow }
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to { background-color: red }
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}
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}
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===
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@mixin inline-animation($duration)
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$name: inline-#{unique-id()}
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@keyframes #{$name}
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@content
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animation-name: $name
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animation-duration: $duration
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animation-iteration-count: infinite
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.pulse
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@include inline-animation(2s)
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from
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background-color: yellow
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to
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background-color: red
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<% end %>
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<% fun_fact do %>
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Interpolation is useful for injecting values into strings, but other than that
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it's rarely necessary in SassScript expressions. You definitely *don't* need
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it to just use a variable in a property value. Instead of writing
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`color: #{$accent}`, you can just write `color: $accent`!
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<% end %>
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<% heads_up do %>
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It's almost always a bad idea to use interpolation with numbers. Interpolation
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returns unquoted strings that can't be used for any further math, and it
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avoids Sass's built-in safeguards to ensure that units are used correctly.
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Sass has powerful [unit arithmetic][] that you can use instead. For example,
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instead of writing `#{$width}px`, write `$width * 1px`—or better yet, declare
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the `$width` variable in terms of `px` to begin with. That way if `$width`
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already has units, you'll get a nice error message instead of compiling bogus
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CSS.
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[unit arithmetic]: values/numbers#units
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<% end %>
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## Quoted Strings
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In most cases, interpolation injects the exact same text that would be used if
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the expression were used as a [property value][]. But there is one exception:
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the quotation marks around quoted strings are removed (even if those quoted
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strings are in lists). This makes it possible to write quoted strings that
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contain syntax that's not allowed in SassScript (like selectors) and interpolate
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them into style rules.
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[property value]: style-rules/declarations
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<% example do %>
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.example {
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unquoted: #{"string"};
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}
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===
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.example
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unquoted: #{"string"}
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<% end %>
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<% heads_up do %>
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While it's tempting to use this feature to convert quoted strings to unquoted
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strings, it's a lot clearer to use the [`string.unquote()` function][].
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Instead of `#{$string}`, write `string.unquote($string)`!
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[`string.unquote()` function]: modules/string#unquote
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<% end %>
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