Sass meta.feature-exists() Function

What You’ll Learn

meta.feature-exists() belongs to the built-in sass:meta module. It once answered “does this compiler support feature X?” This page explains the recognized feature strings, why the API is deprecated, what to use instead, and five examples so you can read and remove legacy code safely.

What Is meta.feature-exists()?

Years ago, Sass implementations differed. Authors used feature-exists("at-error") (and similar checks) to branch stylesheets for older compilers. Official docs: the function returns whether the current implementation supports $feature.

Today Dart Sass is the only officially supported implementation, and it already supports every feature this helper knows about. The Sass team therefore deprecated the function: keeping the checks no longer helps, and the API will disappear in 2.0.

📝 Syntax

@use "sass:meta";

// Deprecated — avoid in new code
meta.feature-exists($feature)

// Legacy global name (also deprecated)
feature-exists($feature)

Parameters

Return value

📚 Recognized Feature Names

Official docs list these strings (and return false for anything else):

📦 Loading sass:meta

// Namespaced (still deprecated)
@use "sass:meta";
$ok: meta.feature-exists("at-error");

// as * (still deprecated)
@use "sass:meta" as *;
$ok: feature-exists("at-error");

// Legacy global (still deprecated)
$ok: feature-exists("at-error");

⏳ Deprecation Timeline

On newer Dart Sass CLIs you can silence this specific warning temporarily with --silence-deprecation=feature-exists, but removing the calls is the real fix.

🚀 What To Use Instead

🛠 Compatibility

This is about Sass compilers, not browsers. Feature detection runs at compile time.

Examples Gallery

These examples show how the deprecated API behaved so you can recognize it in old code. Prefer deleting these patterns in real projects. Open View Compiled CSS for verified output.

@use "sass:meta";

// Deprecated — for learning / migration only
.root {
  --at-error: #{meta.feature-exists("at-error")};
  --unrecognized: #{meta.feature-exists("unrecognized")};
}

.root {
  --at-error: true;
  --unrecognized: false;
}

@use "sass:meta";

.features {
  --global-variable-shadowing: #{meta.feature-exists("global-variable-shadowing")};
  --extend-selector-pseudoclass: #{meta.feature-exists("extend-selector-pseudoclass")};
  --units-level3: #{meta.feature-exists("units-level3")};
  --at-error: #{meta.feature-exists("at-error")};
  --custom-property: #{meta.feature-exists("custom-property")};
}

.features {
  --global-variable-shadowing: true;
  --extend-selector-pseudoclass: true;
  --units-level3: false;
  --at-error: true;
  --custom-property: true;
}

@use "sass:meta";

@mixin assert-positive($n) {
  @if meta.feature-exists("at-error") {
    @if $n <= 0 {
      @error "#{$n} must be positive";
    }
  }
  width: $n;
}

.ok {
  @include assert-positive(40px);
}

.ok {
  width: 40px;
}

@use "sass:meta";
@use "sass:math";

// Prefer member detection (or no check at all) instead of feature-exists
@mixin power-width($base, $exp) {
  @if meta.function-exists("pow", $module: "math") {
    width: math.pow($base, $exp) * 1px;
  } @else {
    width: $base * $exp * 1px; // very old fallback — rarely needed now
  }
}

.box {
  @include power-width(2, 4);
}

.box {
  width: 16px;
}

@use "sass:meta";

.probe {
  --modules: #{meta.feature-exists("modules")};
  --at-use: #{meta.feature-exists("at-use")};
  --typo-at-erorr: #{meta.feature-exists("at-erorr")};
}

.probe {
  --modules: false;
  --at-use: false;
  --typo-at-erorr: false;
}

🚀 When You Still See It

• Legacy libraries — old mixins gated on at-error or units-level3.
• Multi-compiler era code — stylesheets written when LibSass / Ruby Sass differed.
• Deprecation cleanups — search for feature-exists before upgrading to Dart Sass 2.0.
• Learning history — understand why modern Sass prefers member detection instead.

⚠️ Common Pitfalls

• Adding it to new code — it is deprecated and will break in Dart Sass 2.0.
• Assuming every Sass feature has a flag — modules, @use, etc. were never listed.
• Typos return false — silent false negatives look like “unsupported.”
• Silencing forever — --silence-deprecation is temporary, not a fix.
• Confusing with browser feature queries — this never checked CSS browser support.

💡 Best Practices