Sass: Pseudo `undefined` value to distinguish `null`. #sass

SassMeister-input.scss

// ----
// Sass (v3.4.9)
// Compass (v1.0.1)
// ----

// Sass: Pseudo `undefined` value to distinguish `null`.
//
// http://twitter.com/whizark
//
// Other ideas
// https://github.com/whizark/xass#ideas 

// Function
@function undefined() {
  @if not global-variable-exists('-undefined') {
    $-undefined: unique-id() !global;
  }
  
  @return $-undefined;
}

// Use case
@function value-of($value: undefined()) {
  @if $value == undefined() {
    // do something.

    @return 'undefined';
  }
  
  @return $value;
}

.test
{
  test: inspect(value-of());
  test: inspect(value-of(null));
}

SassMeister-output.css

.test {
  test: "undefined";
  test: null;
}