The short way

var webpack = require("webpack");

// returns a Compiler instance
webpack({
    // configuration
}, function(err, stats) {
    // ...
});

The long way

var webpack = require("webpack");

// returns a Compiler instance
var compiler = webpack({
    // configuration
});

compiler.run(function(err, stats) {
    // ...
});
// or
compiler.watch({ // watch options:
    aggregateTimeout: 300, // wait so long for more changes
    poll: true // use polling instead of native watchers
    // pass a number to set the polling interval
}, function(err, stats) {
    // ...
});

Compiler

An instance of Compiler has the following methods

compiler.run(callback) - Builds the bundle(s). It makes an incremental build.

  • callback(err, stats) - A function that will be called with the build is complete.

var watcher = compiler.watch(watchOptions, handler) - Builds the bundle(s) then starts the watcher, which rebuilds bundles whenever their source files change. Returns a Watching instance. Note: since this will automatically run an initial build, so you only need to run watch (and not run).

  • watchOptions
    • watchOptions.aggregateTimeout - After a change the watcher waits that time (in milliseconds) for more changes. Default: 300.
    • watchOptions.poll - The watcher uses polling instead of native watchers. true uses the default interval, a number specifies a interval in milliseconds. Default: undefined (automatic).
  • handler(err, stats) - A function that will be called when a build has been completed, or an error or warning has occurred. (Note that handler is called multiple times. It even can occur that handler is called for the same bundle multiple times. In this cases webpack is not sure about changes and rebuilds.)

Watching

An instance of Watching has the following method:

watcher.close(callback) - stops the watcher.

  • callback - A function that’s called when the watcher has closed.

stats

The Stats object exposes these methods:

stats.hasErrors()

Returns true if there were errors while compiling.

stats.hasWarnings()

Returns true if there were warnings while compiling.

stats.toJson(options)

Return information as JSON object.

There are a few different logging levels, pass these as options (e.g. `stats.toJson(“verbose”)):

"none" (or false) output nothing

"errors-only" only output when errors happen

"minimal" only output when errors or a new compilation happen

"normal" (or true) standard output

"verbose" output all the information webpack has

For more granular control, pass an object that can have these booleans set:

options.context (string) context directory for request shortening

options.hash add the hash of the compilation

options.version add webpack version information

options.timings add timing information

options.assets add assets information

options.chunks add chunk information (setting this to false allows for a less verbose output)

options.chunkModules add built modules information to chunk information

options.modules add built modules information

options.children add children information

options.cached add also information about cached (not built) modules

options.reasons add information about the reasons why modules are included

options.source add the source code of modules

options.errorDetails add details to errors (like resolving log)

options.chunkOrigins add the origins of chunks and chunk merging info

options.modulesSort (string) sort the modules by that field

options.chunksSort (string) sort the chunks by that field

options.assetsSort (string) sort the assets by that field

Here is an example of the resulting JSON.

Note: If you want to extract the asset name for generating the HTML page, use the assetsByChunkName property, which contains an object mapping chunkName to asset name(s) (it’s a string or an array of strings).

stats.toString(options)

Returns a formatted string of the result.

options are the same as options in toJson.

options.colors With console colors

This is an example of how stats.toString can be used:

var webpack = require("webpack");
webpack({
    // configuration
}, function(err, stats) {
        if (err) { throw new gutil.PluginError('webpack:build', err); }
        gutil.log('[webpack:build]', stats.toString({
            chunks: false, // Makes the build much quieter
            colors: true
        }));
});

error handling

to handle all errors and warnings with the node.js API you need to test err, stats.errors and stats.warnings:

var webpack = require("webpack");
webpack({
    // configuration
}, function(err, stats) {
    if(err)
        return handleFatalError(err);
    var jsonStats = stats.toJson();
    if(jsonStats.errors.length > 0)
        return handleSoftErrors(jsonStats.errors);
    if(jsonStats.warnings.length > 0)
        handleWarnings(jsonStats.warnings);
    successfullyCompiled();
});

compile to memory

var MemoryFS = require("memory-fs");
var webpack = require("webpack");

var fs = new MemoryFS();
var compiler = webpack({ ... });
compiler.outputFileSystem = fs;
compiler.run(function(err, stats) {
  // ...
  var fileContent = fs.readFileSync("...");
});
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