Breaking Change: Slash as Division

Sass currently treats / as a division operation in some contexts and a separator in others. This makes it difficult for Sass users to tell what any given / will mean, and makes it hard to work with new CSS features that use / as a separator.

Compatibility:
Dart Sass
partial
LibSass
✗
Ruby Sass
✗

Today, Sass uses complex heuristics to figure out whether a / should be treated as division or a separator. Even then, as a separator it just produces an unquoted string that’s difficult to inspect from within Sass. As more and more CSS features like CSS Grid and the new rgb() and hsl() syntax use / as a separator, this is becoming more and more painful to Sass users.

Because Sass is a CSS superset, we’re matching CSS’s syntax by redefining / to be only a separator. / will be treated as a new type of list separator, similar to how , works today. Division will instead be written using the new math.div() function. This function will behave exactly the same as / does today.

This deprecation does not affect uses of / inside calc() expressions.

Playground

SCSS Syntax

@use "sass:math";

// Future Sass, doesn't work yet!
.item3 {
  $row: span math.div(6, 2) / 7; // A two-element slash-separated list.
  grid-row: $row;
}
Playground

Sass Syntax

@use "sass:math"

// Future Sass, doesn't work yet!
.item3
  $row: span math.div(6, 2) / 7 // A two-element slash-separated list.
  grid-row: $row

CSS Output

.item3 {
  grid-row: span 3 / 7;
}

Transition PeriodTransition Period permalink

Compatibility (math.div() and list.slash()):
Dart Sass
since 1.33.0
LibSass
✗
Ruby Sass
✗

To ease the transition, we’ve begun by adding the math.div() function. The / operator still does division for now, but it also prints a deprecation warning when it does so. Users should switch all division to use math.div() instead.

💡 Fun fact:

Remember, you can silence deprecation warnings from libraries you don’t control! If you’re using the command-line interface you can pass the --quiet-deps flag, and if you’re using the JavaScript API you can set the quietDeps option to true.

Playground

SCSS Syntax

@use "sass:math";

// WRONG, will not work in future Sass versions.
@debug (12px/4px); // 3

// RIGHT, will work in future Sass versions.
@debug math.div(12px, 4px); // 3
Playground

Sass Syntax

@use "sass:math"

// WRONG, will not work in future Sass versions.
@debug (12px/4px) // 3

// RIGHT, will work in future Sass versions.
@debug math.div(12px, 4px) // 3

Slash-separated lists will also be available in the transition period. Because they can’t be created with / yet, the list.slash() function will be added to create them. You will also be able to pass "slash" as the $separator to the list.join() function and the list.append() function.

Playground

SCSS Syntax

@use "sass:list";
@use "sass:math";

.item3 {
  $row: list.slash(span math.div(6, 2), 7);
  grid-row: $row;
}
Playground

Sass Syntax

@use "sass:list"
@use "sass:math"

.item3
  $row: list.slash(span math.div(6, 2), 7)
  grid-row: $row

CSS Output

.item3 {
  grid-row: span 3 / 7;
}
Compatibility (First-class calc):
Dart Sass
since 1.40.0
LibSass
✗
Ruby Sass
✗

Alternatively, users can wrap division operations inside a calc() expression, which Sass will simplify to a single number.

Playground

SCSS Syntax

// WRONG, will not work in future Sass versions.
@debug (12px/4px); // 3

// RIGHT, will work in future Sass versions.
@debug calc(12px / 4px); // 3
Playground

Sass Syntax

// WRONG, will not work in future Sass versions.
@debug (12px/4px) // 3

// RIGHT, will work in future Sass versions.
@debug calc(12px / 4px) // 3

Automatic MigrationAutomatic Migration permalink

You can use the Sass migrator to automatically update your stylesheets to use math.div() and list.slash().

$ npm install -g sass-migrator
$ sass-migrator division **/*.scss

Can I Silence the Warnings?Can I Silence the Warnings? permalink

Sass provides a powerful suite of options for managing which deprecation warnings you see and when.

Terse and Verbose ModeTerse and Verbose Mode permalink

By default, Sass runs in terse mode, where it will only print each type of deprecation warning five times before it silences additional warnings. This helps ensure that users know when they need to be aware of an upcoming breaking change without creating an overwhelming amount of console noise.

If you run Sass in verbose mode instead, it will print every deprecation warning it encounters. This can be useful for tracking the remaining work to be done when fixing deprecations. You can enable verbose mode using the --verbose flag on the command line, or the verbose option in the JavaScript API.

⚠️ Heads up!

When running from the JS API, Sass doesn’t share any information across compilations, so by default it’ll print five warnings for each stylesheet that’s compiled. However, you can fix this by writing (or asking the author of your favorite framework’s Sass plugin to write) a custom Logger that only prints five errors per deprecation and can be shared across multiple compilations.

Silencing Deprecations in DependenciesSilencing Deprecations in Dependencies permalink

Sometimes, your dependencies have deprecation warnings that you can’t do anything about. You can silence deprecation warnings from dependencies while still printing them for your app using the --quiet-deps flag on the command line, or the quietDeps option in the JavaScript API.

For the purposes of this flag, a "dependency" is any stylesheet that’s not just a series of relative loads from the entrypoint stylesheet. This means anything that comes from a load path, and most stylesheets loaded through custom importers.

Silencing Specific DeprecationsSilencing Specific Deprecations permalink

If you know that one particular deprecation isn’t a problem for you, you can silence warnings for that specific deprecation using the --silence-deprecation flag on the command line, or the silenceDeprecations option in the JavaScript API.

⚠️ Heads up!

This option is only available in the modern JS API.