meta.content-exists() returns a boolean: whether the current mixin was passed a @content block when it was included. Load it with @use "sass:meta".
Inside a mixin, @debug meta.content-exists() prints false for a bare @include, and true when the include has a { ... } content block.
Official docs: calling content-exists() outside a mixin throws an error. Keep it inside mixin bodies.
content-exists asks “did this include pass content?” meta.accepts-content asks “can this mixin value take content?”
@use "sass:meta";
meta.content-exists(); //=> boolean (only inside a mixin)
@mixin debug-content-exists {
@debug meta.content-exists();
@content;
}
@include debug-content-exists; // false
@include debug-content-exists { // true
// Content!
}
// Global alias (legacy): content-exists()
// Prefer meta.content-exists after @use "sass:meta"Pattern: inside a mixin → check content-exists → branch defaults vs @content.
Two related helpers, different questions:
| Helper | Asks | Where |
|---|---|---|
meta.content-exists() | Did this include pass a content block? | Only inside a mixin |
meta.accepts-content($mixin) | Can this mixin value take @content? | Anywhere you have a mixin value |
Empty @include m {} | Still counts as content passed | content-exists → true |
Bare @include m; | No content block | content-exists → false |
Use @if meta.content-exists() to emit fallback CSS when callers omit a content block.
Examples use @use "sass:meta". Open View Compiled CSS for verified output (matches official Sass docs behavior).
A bare include reports false.
@use "sass:meta";
@mixin debug-content-exists {
--passed: #{meta.content-exists()};
@content;
}
.no-block {
@include debug-content-exists;
}content-exists is false.@content emits nothing.Passing a content block reports true.
@use "sass:meta";
@mixin debug-content-exists {
--passed: #{meta.content-exists()};
@content;
}
.with-block {
@include debug-content-exists {
color: green;
}
}content-exists is true.@content inserts color: green.@include m {} passes a block even when it is empty.
@use "sass:meta";
@mixin check {
--passed: #{meta.content-exists()};
@content;
}
.empty {
@include check {}
}true.@content.Branch on content-exists for fallback styles.
@use "sass:meta";
@mixin optional {
@if meta.content-exists() {
.inner {
@content;
}
} @else {
outline: 1px dashed gray;
}
}
.a {
@include optional;
}
.b {
@include optional {
color: blue;
}
}.inner.meta.accepts-contentCapability of the mixin vs whether this include passed content.
@use "sass:meta";
@mixin wrap {
--can: #{meta.accepts-content(meta.get-mixin("wrap"))};
--passed: #{meta.content-exists()};
@content;
}
.no-block {
@include wrap;
}
.with-block {
@include wrap {
color: green;
}
}--can stays true for both includes.--passed depends on the caller.Most content-exists bugs are calling it outside a mixin or confusing it with accepts-content.
Outside a mixin, Sass throws. Do not call it at the root of a stylesheet or inside a plain function.
@include m {} is true. Missing braces is false.
Before meta.apply, use meta.accepts-content.
Global content-exists() still exists; new projects should use meta.content-exists.
Prefer the module form with current Dart Sass.
| API | Status |
|---|---|
meta.content-exists() | Dart Sass via @use "sass:meta" |
Global content-exists() | Legacy; prefer module form |
| Where | Inside a mixin only |
| Return type | Boolean |
Compile with the Dart Sass CLI.
@content?One line: when a mixin needs to know if the caller passed @content, call meta.content-exists().
Practical checklist:
1. @use "sass:meta"
2. Call only inside a mixin
3. Branch on meta.content-exists()
4. Remember empty {} still counts as true
5. Use accepts-content for mixin-value capabilityCheck whether the compiler supports a named Sass feature (deprecated helper).
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