Styleloader

Styleloader is a webpack loader that enables importing CSS files in JavaScript bundles and injecting the resulting styles into the document at runtime. It converts CSS import statements into JavaScript that, when executed in the browser, creates a style element and appends it to the document head so that styles take effect immediately. It is commonly used together with css-loader, which resolves @import and url() statements inside CSS.

In a typical webpack setup, CSS files are processed by combining style-loader and css-loader, so that CSS imports in JavaScript modules are resolved and then inserted into the page as needed. This approach supports rapid development and hot module replacement, allowing CSS changes to be reflected without a full page reload.

Style-loader can be customized with options that affect how the styles are injected. Options may control the insertion point in the DOM, whether a single style tag is reused (singleton) or multiple tags are created, and additional attributes on the created style tags. The exact option names and capabilities vary by version, but the general goal is to provide flexibility for development workflows and browser compatibility.

Limitations include reliance on client-side execution; it is not suitable for server-side rendering without additional tooling. For production builds that require extracted CSS as separate files, developers often replace style-loader with plugins such as mini-css-extract-plugin to generate standalone CSS assets. Overall, style-loader remains a common tool in the Webpack ecosystem for handling CSS imports during development.