Webpack is a static module bundler for modern JavaScript applications, primarily responsible for analyzing project structure, identifying JavaScript modules and other languages that browsers cannot directly execute (such as TypeScript), and converting and bundling them into appropriate formats for browser consumption.
Webpack's workflow is primarily divided into the following stages:
Initialization
Upon starting, Webpack reads configuration parameters from the configuration file (defaulting to webpack.config.js), merges command-line arguments, and constructs the final configuration object.
Compiling
Webpack initiates the compilation of the entire project. In this phase, it recursively resolves all dependencies based on the entry configuration. The entry property specifies the entry file(s), which can be singular or multiple.
Building
For each dependency, Webpack employs the appropriate loader to process files. For instance, it uses babel-loader for JavaScript files, css-loader for CSS files, and file-loader for images and other resources. Loaders enable Webpack to handle non-JavaScript files (as Webpack itself only understands JavaScript).
Output
Following loading and transformation, Webpack writes the processed files to the file system according to the output configuration. Typically, it outputs bundle.js or other custom-named files to the project's dist directory.
Optimizing
On the generated files, Webpack can perform optimizations such as code minification and code splitting for lazy loading. These are implemented via plugins, such as UglifyJsPlugin and SplitChunksPlugin.
Emitting
All resource files are emitted to the designated directory, completing Webpack's process.
Example
For instance, in a project with an entry file src/index.js, Webpack parses this file and resolves its dependencies. If index.js references src/print.js, Webpack proceeds to resolve print.js's dependencies.
Assuming index.js utilizes ES6 syntax and .scss style files, during the build phase, Webpack employs babel-loader to transpile ES6 to ES5, sass-loader to convert SCSS to CSS, and integrates css-loader with style-loader to inject CSS into JavaScript, enabling styles to be added to the DOM through JavaScript.
In the optimization phase, plugins can analyze the code, eliminate dead code (unused code), minify and obfuscate output files to reduce size and enhance load performance.
Ultimately, during the output phase, Webpack generates bundle.js in the dist directory, which includes all application code and the CSS code bundled from all styles.
This outlines the fundamental workflow of Webpack. Its power stems from extensibility, enabling it to accommodate diverse complex project needs via configuration files and the plugin system.