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Native ES Module Loading (ESM): Vite leverages native ES Modules (ESM) supported by modern browsers to serve modules. In development mode, Vite functions as a browser-native module server, bypassing the need for bundling and building code; instead, it directly loads modules using
<script type="module">. This enables rapid server startup, and when a module is requested, the browser loads only the required modules instead of the entire application's bundled output. -
On-Demand Compilation: When using traditional bundlers like Webpack, all dependencies of the application must be bundled at startup, including third-party libraries and application code. This process takes time, especially for large applications. In contrast, Vite employs an on-demand compilation strategy in development mode, meaning it compiles and processes a file only when it is requested. This approach significantly reduces startup time and enables rapid response to code hot updates.
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Cache Optimization: Vite optimizes the pre-bundling process for dependencies. During the first run, it compiles all dependencies into ESM and caches the results. In subsequent startups, if there are no changes to dependencies, it directly uses the cached results instead of recompiling, further improving startup speed.
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Fast Hot Module Replacement (HMR): Vite's Hot Module Replacement (HMR) is module-level, meaning only the changed file and its dependency chain are reloaded and compiled when a file changes. This is significantly faster than bundlers like Webpack performing a full refresh.
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Efficient Pre-bundling of Dependencies: For certain complex dependencies (such as CommonJS modules or libraries that depend on other modules), Vite uses esbuild to pre-bundle these dependencies. esbuild, written in Go, is significantly faster than JavaScript-based bundlers like Webpack and Rollup.
For example, consider a large application with hundreds of modules. With traditional bundlers, even modifying a single module requires re-bundling the entire application, which can take tens of seconds or longer. With Vite, modifying a single module only recompiles and returns that module, allowing you to see changes almost immediately, greatly enhancing development efficiency.
Overall, Vite achieves fast startup by eliminating unnecessary bundling steps during development, adopting more modern module loading approaches, and leveraging intelligent caching and pre-compilation strategies. These design principles enable Vite to provide an extremely responsive development experience.