The Compiler module is the main engine that creates a compilation instance with all the options passed through the CLI or Node API. It extends the Tapable class in order to register and call plugins. Most user facing plugins are first registered on the Compiler.

This module is exposed as webpack.Compiler and can be used directly. See this example for more information.

When developing a plugin for webpack, you might want to know where each hook is called. To learn this, search for hooks.<hook name>.call across the webpack source

Watching

The Compiler supports watching which monitors the file system and recompiles as files change. When in watch mode, the compiler will emit the additional events such as watchRun, watchClose, and invalid. This is typically used in development, usually under the hood of tools like webpack-dev-server, so that the developer doesn't need to re-compile manually every time. Watch mode can also be entered via the CLI.

Hooks

The following lifecycle hooks are exposed by the compiler and can be accessed as such:

compiler.hooks.someHook.tap('MyPlugin', (params) => {
  /* ... */
});

Depending on the hook type, tapAsync and tapPromise may also be available.

For the description of hook types, see the Tapable docs.

entryOption

SyncBailHook

Called after the entry configuration from webpack options has been processed.

• Callback Parameters: context, entry

compiler.hooks.entryOption.tap('MyPlugin', (context, entry) => {
  /* ... */
});

Parameters: context, entry

afterPlugins

SyncHook

Called after setting up initial set of internal plugins.

• Callback Parameters: compiler

afterResolvers

SyncHook

Triggered after resolver setup is complete.

• Callback Parameters: compiler

environment

SyncHook

Called while preparing the compiler environment, right after inizializing the plugins in the configuration file.

afterEnvironment

SyncHook

Called right after the environment hook, when the compiler environment setup is complete.

beforeRun

AsyncSeriesHook

Adds a hook right before running the compiler.

• Callback Parameters: compiler

run

AsyncSeriesHook

Hook into the compiler before it begins reading records.

• Callback Parameters: compiler

watchRun

AsyncSeriesHook

Executes a plugin during watch mode after a new compilation is triggered but before the compilation is actually started.

• Callback Parameters: compiler

normalModuleFactory

SyncHook

Called after a NormalModuleFactory is created.

• Callback Parameters: normalModuleFactory

contextModuleFactory

SyncHook

Runs a plugin after a ContextModuleFactory is created.

• Callback Parameters: contextModuleFactory

beforeCompile

AsyncSeriesHook

Executes a plugin after compilation parameters are created.

• Callback Parameters: compilationParams

The compilationParams variable is initialized as follows:

compilationParams = {
  normalModuleFactory,
  contextModuleFactory,
  compilationDependencies
};

This hook can be used to add/modify the compilation parameters:

compiler.hooks.beforeCompile.tapAsync('MyPlugin', (params, callback) => {
  params['MyPlugin - data'] = 'important stuff my plugin will use later';
  callback();
});

compile

SyncHook

Called right after beforeCompile, before a new compilation is created.

• Callback Parameters: compilationParams

thisCompilation

SyncHook

Executed while initializing the compilation, right before emitting the compilation event.

• Callback Parameters: compilation, compilationParams

compilation

SyncHook

Runs a plugin after a compilation has been created.

• Callback Parameters: compilation, compilationParams

make

AsyncParallelHook

Executed before finishing the compilation.

• Callback Parameters: compilation

afterCompile

AsyncSeriesHook

Called after finishing and sealing the compilation.

• Callback Parameters: compilation

shouldEmit

SyncBailHook

Called before emitting assets. Should return a boolean telling whether to emit.

• Callback Parameters: compilation

compiler.hooks.shouldEmit.tap('MyPlugin', (compilation) => {
  // return true to emit the output, otherwise false
  return true;
});

emit

AsyncSeriesHook

Executed right before emitting assets to output dir.

• Callback Parameters: compilation

afterEmit

AsyncSeriesHook

Called after emitting assets to output directory.

• Callback Parameters: compilation

assetEmitted

AsyncSeriesHook

Allows to get byte content of emitted asset. Available since webpack v4.39.0

• Callback Parameters: file, content

done

AsyncSeriesHook

Executed when the compilation has completed.

• Callback Parameters: stats

failed

SyncHook

Called if the compilation fails.

• Callback Parameters: error

invalid

SyncHook

Executed when a watching compilation has been invalidated.

• Callback Parameters: fileName, changeTime

watchClose

SyncHook

Called when a watching compilation has stopped.

infrastructureLog

SyncBailHook

Allows to use infrastructure logging when enabled in the configuration via infrastructureLogging option.

• Callback Parameters: name, type, args

log

SyncBailHook

Allows to log into stats when enabled, see stats.logging, stats.loggingDebug and stats.loggingTrace options.

• Callback Parameters: origin, logEntry