@import to @use migration in SASS - Performance & Optimization

Performance: @import to @use migration

MEDIUM IMPACT

This affects CSS build time and runtime style calculation by improving modularity and reducing redundant style processing.

Including shared styles in multiple Sass files

SASS

@use 'variables' as *;
@use 'mixins';

@use loads each module once and namespaces variables, avoiding duplication and improving build efficiency.

📈 Performance Gainsingle style processing per module, smaller CSS output

Including shared styles in multiple Sass files

SASS

@import 'variables';
@import 'mixins';
@import 'variables';

Repeated @import causes styles and variables to be processed multiple times, increasing build size and slowing compilation.

📉 Performance Costtriggers redundant style processing and larger CSS output

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
@import repeated modules	N/A	N/A	Higher due to larger CSS	[X] Bad
@use single module import	N/A	N/A	Lower due to smaller CSS	[OK] Good

Rendering Pipeline

Sass @import causes repeated style inclusion increasing CSS size and style recalculation. @use loads modules once, reducing CSS size and improving style calculation.

→Style Calculation

→Layout

→Paint

⚠️ BottleneckStyle Calculation due to redundant CSS rules

Core Web Vital Affected

LCP

This affects CSS build time and runtime style calculation by improving modularity and reducing redundant style processing.

Optimization Tips

1Use @use to load Sass modules once and avoid duplication.

2Avoid multiple @import of the same file to reduce CSS size.

3Namespace variables with @use to prevent conflicts and improve maintainability.

Performance Quiz - 3 Questions

What is a main performance benefit of using @use instead of @import in Sass?

A It allows inline JavaScript in styles

B Modules are loaded only once, reducing CSS size

C It automatically minifies CSS

D It disables CSS caching

DevTools: Network

How to check: Open DevTools > Network tab > Reload page > Check CSS file size and number of CSS files loaded

What to look for: Smaller CSS file size and fewer duplicate styles indicate good @use usage