When is PostCSS used together with preprocessors?
PostCSS is used together with preprocessors when there is a need to separate development tasks from production tasks. A preprocessor makes writing CSS more convenient, while PostCSS brings the final code to an optimal state for browsers.
When they are combined in practice
1) For cross-browser support after SASS/LESS Even if a project is written in SCSS, without PostCSS you would have to track prefixes by hand. So the chain is usually:
SASS/LESS → CSS → PostCSS (Autoprefixer) → final CSS2) For minifying and optimizing the final CSS
A preprocessor does not minify or clean up code, but PostCSS plugins (for example, cssnano) do this automatically.
3) For using modern CSS features
If new CSS capabilities are used in SCSS, PostCSS with the postcss-preset-env plugin converts them into code compatible with current browsers.
4) For removing unnecessary styles in production
Tools like PurgeCSS only work after the styles have already been generated. That is not a preprocessor's job.
Division of roles
| Stage | Tool | What it does |
|---|---|---|
| development | SASS/LESS | variables, nesting, mixins and convenient syntax |
| build/production | PostCSS | prefixes, minification, cleanup, optimization |
Summary
PostCSS is used together with preprocessors when there is a need to:
- write code conveniently (preprocessor)
- and at the same time ship it to production as clean, optimized and cross-browser as possible (PostCSS)
In other words, the tools do not compete; they complement each other in a single pipeline.
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