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200 lines
6.8 KiB
Plaintext
200 lines
6.8 KiB
Plaintext
---
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title: Special Functions
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table_of_contents: true
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introduction: >
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CSS defines many functions, and most of them work just fine with Sass’s normal
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function syntax. They’re parsed as function calls, resolved to [plain CSS
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functions](../functions/css), and compiled as-is to CSS. There are a few
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exceptions, though, which have special syntax that can’t just be parsed as a
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[SassScript expression](structure#expressions). All special function calls
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return [unquoted strings](../values/strings#unquoted).
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---
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## `url()`
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The [`url()` function][] is commonly used in CSS, but its syntax is different
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than other functions: it can take either a quoted *or* unquoted URL. Because an
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unquoted URL isn't a valid SassScript expression, Sass needs special logic to
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parse it.
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[`url()` function]: https://developer.mozilla.org/en-US/docs/Web/CSS/url
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If the `url()`'s argument is a valid unquoted URL, Sass parses it as-is,
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although [interpolation][] may also be used to inject SassScript values. If it's
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not a valid unquoted URL—for example, if it contains [variables][] or [function
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calls][]—it's parsed as a normal [plain CSS function call][].
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[interpolation]: ../interpolation
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[variables]: ../variables
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[function calls]: ../at-rules/function
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[plain CSS function call]: ../functions/css
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<% example do %>
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$roboto-font-path: "../fonts/roboto";
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@font-face {
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// This is parsed as a normal function call that takes a quoted string.
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src: url("#{$roboto-font-path}/Roboto-Thin.woff2") format("woff2");
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font-family: "Roboto";
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font-weight: 100;
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}
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@font-face {
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// This is parsed as a normal function call that takes an arithmetic
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// expression.
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src: url($roboto-font-path + "/Roboto-Light.woff2") format("woff2");
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font-family: "Roboto";
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font-weight: 300;
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}
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@font-face {
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// This is parsed as an interpolated special function.
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src: url(#{$roboto-font-path}/Roboto-Regular.woff2) format("woff2");
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font-family: "Roboto";
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font-weight: 400;
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}
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===
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$roboto-font-path: "../fonts/roboto"
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@font-face
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// This is parsed as a normal function call that takes a quoted string.
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src: url("#{$roboto-font-path}/Roboto-Thin.woff2") format("woff2")
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font-family: "Roboto"
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font-weight: 100
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@font-face
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// This is parsed as a normal function call that takes an arithmetic
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// expression.
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src: url($roboto-font-path + "/Roboto-Light.woff2") format("woff2")
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font-family: "Roboto"
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font-weight: 300
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@font-face
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// This is parsed as an interpolated special function.
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src: url(#{$roboto-font-path}/Roboto-Regular.woff2) format("woff2")
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font-family: "Roboto"
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font-weight: 400
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<% end %>
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## `calc()`, `element()`, `progid:...()`, and `expression()`
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The [`calc()`][] and [`element()`][] functions are defined in the CSS spec.
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Because `calc()`'s mathematical expressions conflict with Sass's arithmetic, and
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`element()`'s IDs could be parsed as colors, they need special parsing.
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[`calc()`]: https://developer.mozilla.org/en-US/docs/Web/CSS/calc
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[`element()`]: https://developer.mozilla.org/en-US/docs/Web/CSS/element
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[`expression()`][] and functions beginning with [`progid:`][] are legacy
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Internet Explorer features that use non-standard syntax. Although they're no
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longer supported by recent browsers, Sass continues to parse them for backwards
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compatibility.
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[`expression()`]: https://blogs.msdn.microsoft.com/ie/2008/10/16/ending-expressions/
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[`progid:`]: https://blogs.msdn.microsoft.com/ie/2009/02/19/the-css-corner-using-filters-in-ie8/
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Sass allows *any text* in these function calls, including nested parentheses.
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Nothing is interpreted as a SassScript expression, with the exception that
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[interpolation][] can be used to inject dynamic values.
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<% example do %>
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.logo {
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$width: 800px;
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width: $width;
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position: absolute;
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left: calc(50% - #{$width / 2});
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top: 0;
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}
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===
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.logo
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$width: 800px
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width: $width
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position: absolute
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left: calc(50% - #{$width / 2})
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top: 0
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<% end %>
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## `min()` and `max()`
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<% impl_status(dart: "1.11.0", libsass: false, ruby: false) do %>
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LibSass and Ruby Sass currently *always* parse `min()` and `max()` as Sass
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functions. To create a plain CSS `min()` or `max()` call for those
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implementations, you can write something like `unquote("min(#{$padding},
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env(safe-area-inset-left))")` instead.
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<% end %>
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CSS added support for [`min()` and `max()` functions][] in Values and Units
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Level 4, from where they were quickly adopted by Safari [to support the
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iPhoneX][]. But Sass supported its own [`min()`][] and [`max()`][] functions
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long before this, and it needed to be backwards-compatible with all those
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existing stylesheets. This led for the need for extra-special syntactic
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cleverness.
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[`min()` and `max()` functions]: https://drafts.csswg.org/css-values-4/#calc-notation
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[to support the iPhoneX]: https://webkit.org/blog/7929/designing-websites-for-iphone-x/
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[`min()`]: ../functions/math#min
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[`max()`]: ../functions/math#max
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If a `min()` or `max()` function call is valid plain CSS, it will be compiled to
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a CSS `min()` or `max()` call. "Plain CSS" includes nested calls to
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[`calc()`][], [`env()`][], [`var()`][], `min()`, or `max()`, as well as
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[interpolation][]. As soon as any part of the call contains a SassScript feature
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like [variables][] or [function calls][], though, it's parsed as a call to
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Sass's core `min()` or `max()` function instead.
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[`env()`]: https://developer.mozilla.org/en-US/docs/Web/CSS/env
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[`var()`]: https://developer.mozilla.org/en-US/docs/Web/CSS/var
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<!-- TODO(nweiz): auto-generate this CSS once we're compiling with Dart Sass -->
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<% example do %>
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$padding: 12px;
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.post {
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// Since these max() calls don't use any Sass features other than
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// interpolation, they're compiled to CSS max() calls.
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padding-left: max(#{$padding}, env(safe-area-inset-left));
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padding-right: max(#{$padding}, env(safe-area-inset-right));
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}
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.sidebar {
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// Since these refer to a Sass variable without interpolation, they call
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// Sass's built-in max() function.
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padding-left: max($padding, 20px);
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padding-right: max($padding, 20px);
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}
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===
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$padding: 12px
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.post
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// Since these max() calls don't use any Sass features other than
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// interpolation, they're compiled to CSS max() calls.
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padding-left: max(#{$padding}, env(safe-area-inset-left))
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padding-right: max(#{$padding}, env(safe-area-inset-right))
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.sidebar
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// Since these refer to a Sass variable without interpolation, they call
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// Sass's built-in max() function.
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padding-left: max($padding, 20px)
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padding-right: max($padding, 20px)
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===
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.post {
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padding-left: max(12px, env(safe-area-inset-left));
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padding-right: max(12px, env(safe-area-inset-right));
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}
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.sidebar {
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padding-left: 20px;
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padding-right: 20px;
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}
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<% end %>
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