meta.feature-exists($feature) returns a boolean: whether the current Sass implementation reports support for the named $feature string. Unrecognized names return false. Load it with @use "sass:meta".
meta.feature-exists("at-error") → true · meta.feature-exists("unrecognized") → false.
Official docs say this helper is deprecated and should be avoided. Dart Sass emits deprecation warnings on every call. Prefer deleting checks; modern Dart Sass already covers the capabilities this function gated.
For member detection, use meta.function-exists, meta.mixin-exists, or meta.global-variable-exists.
@use "sass:meta";
meta.feature-exists($feature); //=> boolean (deprecated)
meta.feature-exists("at-error"); // true
meta.feature-exists("unrecognized"); // false
// Global alias (legacy): feature-exists($feature)
// Prefer removing both forms in new projectsPattern for legacy code: read the feature string → understand the boolean → plan removal rather than adding new branches.
Official docs list these feature strings:
| Feature string | Meaning |
|---|---|
global-variable-shadowing | Local variables shadow globals unless marked !global |
extend-selector-pseudoclass | @extend affects selectors nested in pseudo-classes like :not() |
units-level3 | Unit arithmetic supports CSS Values and Units Level 3 units |
at-error | The @error rule is supported |
custom-property | Custom property values only allow interpolation (not full Sass expressions) |
| Any other string | Returns false |
A true/false answer is what that implementation reports for the string. Prefer deleting the check on modern Dart Sass instead of trusting long-term.
Examples show the legacy API for reading older code. Expect deprecation warnings from Dart Sass. Open View Compiled CSS for verified output.
at-error)Modern Dart Sass reports support for @error.
@use "sass:meta";
@debug meta.feature-exists("at-error"); // true
.basic {
--at-error: #{meta.feature-exists("at-error")};
}"at-error".true.Unknown feature names return false.
@use "sass:meta";
@debug meta.feature-exists("unrecognized"); // false
.unknown {
--ok: #{meta.feature-exists("unrecognized")};
}false.What current Dart Sass reports for the classic feature strings.
@use "sass:meta";
.list {
--gvs: #{meta.feature-exists("global-variable-shadowing")};
--extend: #{meta.feature-exists("extend-selector-pseudoclass")};
--units: #{meta.feature-exists("units-level3")};
--error: #{meta.feature-exists("at-error")};
--custom: #{meta.feature-exists("custom-property")};
}true here.units-level3 may report false even on modern Dart Sass.Old libraries sometimes branched on feature support. Prefer deleting the branch.
@use "sass:meta";
.legacy {
@if meta.feature-exists("at-error") {
--can-error: true;
} @else {
--can-error: false;
}
}at-error.@error exists and drop the check.Replace feature probes with targeted meta helpers when you need detection.
@use "sass:meta";
@use "sass:math";
// Instead of meta.feature-exists("…"):
.migrate {
--has-div: #{meta.function-exists("div", $module: "math")};
--has-abs: #{meta.function-exists("abs", $module: "math")};
}function-exists is the supported approach.Most feature-exists bugs are treating a deprecated probe as a long-term public API.
Official docs say avoid it. New projects should never introduce feature-exists.
A listed name can still report false on some compilers (for example units-level3 on current Dart Sass).
There is no registry of new feature names. Custom strings always fail the check.
Use function-exists / mixin-exists / global-variable-exists, or delete the gate.
Still callable today, but deprecated on modern Dart Sass.
| API | Status |
|---|---|
meta.feature-exists() | Deprecated; emits warnings in current Dart Sass |
Global feature-exists() | Legacy; same deprecation |
| Dart Sass 2.0 | Expected to throw / treat global name as CSS |
| Argument | String feature name |
Compile with the Dart Sass CLI.
One line: when you see meta.feature-exists($feature) in old code, plan to remove it rather than extend it.
Practical checklist:
1. Recognize feature-exists as deprecated
2. Expect Dart Sass deprecation warnings
3. Prefer deleting the check on modern Dart Sass
4. Use function-exists / mixin-exists / global-variable-exists instead
5. Do not invent new feature stringsUse the supported way to check whether a function name is defined.
8 people found this page helpful