webpack 4.0.0-alpha.5 feedback

Complete changelog for 4.0.0-alpha.5 compared to version 3:

Items changed from 4.0.0-alpha.4 to 4.0.0-alpha.5 are prefixed with [new]

Big changes

• Environment
  • Node.js 4 is no longer supported. Source Code was upgraded to a higher ecmascript version.
• Usage
  • You have to choose (mode or --mode) between two modes now: production or development
    • production enables all kind of optimizations to generate optimized bundles
    • development enables comments and hint for development and enables the eval devtool
      • WIP: addition hints in development mode
    • production doesn’t support watching, development is optimized for fast incremental rebuilds
    • production also enables module concatenating (Scope Hoisting)
    • You can configure this in detail with the flags in optimization.* (build your custom mode)
    • process.env.NODE_ENV are set to production or development (only in built code, not in config)
    • There is a hidden none mode which disables everything
• Syntax
  • import() always returns a namespace object. CommonJS modules are wrapped into the default export
    • This probably breaks your code, if you used to import CommonJs with import()
• Configuration
  • You no longer need to use these plugins:
    • NoEmitOnErrorsPlugin -> optimization.noEmitOnErrors (on by default in production mode)
    • ModuleConcatenationPlugin -> optimization.concatenateModules (on by default in production mode)
    • NamedModulesPlugin -> optimization.namedModules (on by default in develoment mode)
  • [new] CommonsChunkPlugin was removed -> optimization.splitChunks
• JSON
  • webpack now handles JSON natively
    • You may need to add type: "javascript/auto" when transforming JSON via loader to JS
    • Just using JSON without loader should still work
  • allows to import JSON via ESM syntax
    • unused exports elimination for JSON modules
• Optimization
  • Upgrade uglifyjs-webpack-plugin to v1
    • ES15 support

Big features

• Modules
  • webpack now supports these module types:
    • javascript/auto: (The default one in webpack 3) Javascript module with all module systems enabled: CommonJS, AMD, ESM
    • javascript/esm: EcmaScript modules, all other module system are not available
    • javascript/dynamic: Only CommonJS and, EcmaScript modules are not available
    • json: JSON data, it’s available via require and import
    • webassembly/experimental: WebAssembly modules (currently experimental)
  • javascript/esm handles ESM more strict compared to javascript/auto:
    • Imported names need to exist on imported module
    • Non-ESM can only imported via default import, everything else (including namespace import) emit errors
  • In .mjs modules
    • javascript/esm is used
  • WebAssembly modules
    • can import other modules (JS and WASM)
    • Exports from WebAssembly modules are validated by ESM import
      • You’ll get a warning/error when trying to import a non-existing export from WASM
• Optimization
  • sideEffects: false is now supported in package.json
  • Instead of a JSONP function a JSONP array is used -> async support
  • [new] New optimization.splitChunks option was introduced Details: https://gist.github.com/sokra/1522d586b8e5c0f5072d7565c2bee693
  • [new] Dead branches are now removed by webpack itself
    • Before: Uglify removed the dead code
    • Now: webpack removes the dead code (in some cases)
    • This prevents crashing when import() occur in a dead branch
• Syntax
  • webpackInclude and webpackExclude are supported by the magic comment for import(). They allow to filter files when using a dynamic expression.
  • [new] Using System.import() now emits a warning
    • You can disable the warning with Rule.parser.system: true
    • You can disable System.import with Rule.parser.system: false
• Configuration
  • Resolving can now be configured with module.rules[].resolve. It’s merged with the global configuration.
  • optimization.minimize has been added to switch minimizing on/off
    • By default: on in production mode, off in development mode
  • optimization.minimizer has been added to configurate minimizers and options
  • many config options which support placeholders now also support a function
• Usage
  • Some Plugin options are now validated
    • WIP: Better output, no process exit, stack trace, more plugins
  • CLI has been move to webpack-cli, you need to install webpack-cli to use the CLI
  • The ProgressPlugin (--progress) now displays plugin names
    • At least for plugins migrated to the new plugin system
• Performance
  • UglifyJs now caches and parallizes by default
  • Multiple performance improvements, especially for faster incremental rebuilds
  • performance improvement for RemoveParentModulesPlugin
• Stats
  • Stats can display modules nested in concatenated modules

Features

• Configuration
  • Module type is automatically choosen for mjs, json and wasm extensions. Other extensions need to be configured via module.rules[].type
  • Incorrect options.dependencies configurations now throw error
  • Rule.ident is now allowed by schema
  • sideEffects can be overriden via module.rules
  • output.hashFunction can now be a Constructor to a custom hash function
    • You can provide a non-cryto hash function for performance reasons
  • add output.globalObject config option to allow to choose the global object reference in runtime exitCode
• Runtime
  • Error for chunk loading now includes more information and two new properties type and request.
• Performance
  • webpacks AST can be passed directly from loader to webpack to avoid extra parsing
  • Unused modules are no longer unnecessarly concatenated
  • [new] Add a ProfilingPlugin which write a (Chrome) profile file which includes timings of plugins
  • [new] Migrate to using for of instead of forEach
  • [new] Migrate to using Map and Set instead of Objects
  • [new] Migrate to using includes instead of indexOf
  • [new] Replaced some RegExp with string methods
  • [new] Queue don’t enqueues the same job twice
• Optimization
  • When using more than 25 exports mangled export names are shorter.
  • script tags are no longer text/javascript and async as this are the default values (saves a few bytes)
  • The concatenated module now generates a bit less code
  • constant replacements now don’t need __webpack_require__ and argument is omitted
• Defaults
  • webpack now looks for the .wasm, .mjs, .js and .json extensions in this order
  • output.pathinfo is now on by default in develoment mode
  • in-memory caching is now off by default in production
  • entry defaults to ./src
  • output.path defaults to ./dist
  • Use production defaults when omiting the mode option
• Usage
  • Add detailed progress reporting to SourceMapDevToolPlugin
• Stats
  • Sizes are now shown in kiB instead of kB in Stats
  • [new] entrypoints are now shows by default in Stats
  • [new] chunks now display <{parent}> >{children}< and ={siblings}= in Stats
• Syntax
  • A resource query is supported in context
  • Parser now understand new Foo() expressions
  • Parser can now evaluate **, &, |, ^, >>>, >>, << and ~
  • Referencing entry point name in import() now emits a error instead of a warning
  • [new] Upgraded to acorn 5

Bugfixes

• Generated comments no longer break on */
• webpack no longer modifies the passed options object
• Compiler “watch-run” hook now has the Compiler as first parameter
• add chunkCallbackName to the schema to allow configurating WebWorker template
• Using module.id/loaded now correctly bails out of Module Concatentation (Scope Hoisting)
• OccurenceOrderPlugin now sorts modules in correct order (instead of reversed)
• timestamps for files are read from watcher when calling Watching.invalidate
• Avoid using process.exit and use process.exitCode instead
• fix bluebird warning in webpack/hot/signal
• fix incorrect -! behavior with post loaders
• add run and watchRun hooks for MultiCompiler
• [new] this is now undefined in ESM
• [new] Initial chunks no longer contribute to chunkhash of runtime chunk and hashes don’t occur in chunk hash map
• [new] VariableDeclaration are correctly identified as var, const or let
• [new] Parser now parse the source code with the correct source type (module/script) when the module type javascript/dynamic or javascript/module is used.

Internal changes

• Replaced plugin calls with tap calls (new plugin system)
• Migrated many deprecated plugins to new plugin system API
• added buildMeta.exportsType: "default" for json modules
• Remove unused methods from Parser (parserStringArray, parserCalculatedStringArray)
• Remove ability to clear BasicEvaluatedExpression and to have multiple types

Removed features

• removed module.loaders
• removed loaderContext.options
• removed Compilation.notCacheable flag
• removed NoErrorsPlugin
• removed Dependency.isEqualResource
• removed NewWatchingPlugin
• [new] removed CommonsChunkPlugin

Breaking changes for plugins/loaders

• new plugin system
  • plugin method is backward-compatible
  • Plugins should use Compiler.hooks.xxx.tap(<plugin name>, fn) now
• New major version of enhanced-resolve
• Templates for chunks may now generate multiple assets
• Chunk.chunks/parents/blocks are no longer Arrays. A Set is used internally and there are methods to access it.
• Parser.scope.renames and Parser.scope.definitions are no longer Objects/Arrays, but Map/Sets.
• Parser uses StackedSetMap (LevelDB-like datastructure) instead of Arrays
• Compiler.options is no longer set while applying plugins
• Harmony Dependencies has changed because of refactoring
• Dependency.getReference() may now return a weak property. Dependency.weak is now used by the Dependency base class and returned in the base impl of getReference()
• Constructor arguments changed for all Modules
• Merged options into options object for ContextModule and resolveDependencies
• Changed and renamed dependencies for `import()
• Moved Compiler.resolvers into Compiler.resolverFactory accessible with plugins
• Dependency.isEqualResource has been replaced with Dependency.getResourceIdentifier
• Methods on Template are now static
• A new RuntimeTemplate class has been added and outputOptions and requestShortener has been moved to this class
  • Many methods has been updated to use the RuntimeTemplate instead
  • We plan to move code which accesses the runtime to this new class
• Module.meta has been replaced with Module.buildMeta
• Module.buildInfo and Module.factoryMeta have been added
• Some properties of Module have been moved into the new objects
• added loaderContext.rootContext which points to the context options. Loaders may use it to make stuff relative to the application root.
• add this.hot flag to loader context when HMR is enabled
• buildMeta.harmony has been replaced with buildMeta.exportsType: "namespace
• [new] The chunk graph has changed:
  • Before: Chunks were connected with parent-child-relationships.
  • Now: ChunkGroups are connected with parent-child-relationships. ChunkGroups contain Chunks in order.
  • Before: AsyncDependenciesBlocks reference a list of Chunks in order.
  • Now: AsyncDependenciesBlocks reference a single ChunkGroup.

Migration

Node.js

If you are still using Node.js 4 or smaller:

Install Node.js 8. You could also install Node.js 6 but it’s slower (2x).

CLI

To use the command line interface:

yarn add -D webpack-cli

or

npm install -D webpack-cli

Configuration

  // webpack.production.config.js
  module.exports = {
+   mode: "production",
    plugins: [
-     new UglifyJsPlugin(/* ... */),
-     new webpack.DefinePlugin({ "process.env.NODE_ENV": JSON.stringify("production") }),
-     new webpack.optimize.ModuleConcatenationPlugin(),
-     new webpack.NoEmitOnErrorsPlugin()
    ]
  }

  // webpack.development.config.js
  module.exports = {
+   mode: "development",
    plugins: [
-     new webpack.NamedModulesPlugin(),
-     new webpack.DefinePlugin({ "process.env.NODE_ENV": JSON.stringify("development") }),
    ]
  }

import() CommonJs

import() now always returns the namespace object and not the exports directly for non-ESM.

- import("./commonjs").then(exports => {
+ import("./commonjs").then({ default: exports } => {
    // ...
  })

Note: ESM modules are not affected.

Note: Babel transpiled ESM (__esModule: true) will work in .js modules (javascript/auto), but not in .mjs modules.

Note: For JSON the same is true, but as JSON modules also export each property as exports you could pick property via destruction.

CommonsChunkPlugin

The following guides try to give 1 to 1 translations for the CommonsChunkPlugin. This does not neccessary fit bet pratices.

Best practise

optimization: {
  splitChunks: {
    chunks: "all"
  }
}

You need to generate the HTML from stats json. Use the entrypoints property from Stats to know which files to include for each entrypoint.

Initial vendor chunk

entry: {
  vendor: ["react", "lodash", "angular", ...]
}
new CommonsChunkPlugin({
  name: "vendors",
})

entry: {
  vendor: ["react", "lodash", "angular", ...]
},
optimization: {
  splitChunks: {
    cacheGroups: {
      vendor: {
        chunks: "initial",
        test: "vendor",
        name: "vendor",
        enforce: true
      }
    }
  }
}

Alternative:

optimization: {
  splitChunks: {
    cacheGroups: {
      vendor: {
        chunks: "initial",
        test: path.resolve(__dirname, "node_modules")
        name: "vendor",
        enforce: true
      }
    }
  }
}

Difference: This includes all used modules from node_modules and allows tree shaking.

Note: You don’t need to specify a entry for the alternative.

Commons chunk

new CommonsChunkPlugin({
  name: "commons",
  minChunks: 3
})

optimization: {
  splitChunks: {
    cacheGroups: {
      commons: {
        chunks: "initial",
        minChunks: 3,
        name: "commons",
        enforce: true
      }
    }
  }
}

Better vendor chunk

new CommonsChunkPlugin({
  name: "vendors",
  minChunks: module => {
    return module.resource && /react|angluar|lodash/.test(module.resource);
  }
})

optimization: {
  splitChunks: {
    cacheGroups: {
      vendor: {
        test: /react|angluar|lodash/
        chunks: "initial",
        name: "vendor",
        enforce: true
      }
    }
  }
}

Async commons chunk

new CommonsChunkPlugin({
  async: true,
  // ...
})

Just omit it. The defaults already do such optimization.

Deep Children

Anything with deepChildren: true and no async.

See configuration above but use chunks: "all".

Loaders consuming JSON

  module.rules: [
    {
      test: /\.special\.json$/,
+     type: "javascript/auto",
      use: "special-loader"
    }
  ]

[Andarist]

Super cool, list of changes is amazing ❤️ it even has a thing that I was about to request last week but didn’t have time yet to create an issue (“[new] Dead branches are now removed by webpack itself”)

[vladshcherbin]

@sokra Is it somehow possible to remove webpack webpackBootstrap code from bundle in webpack 4? Rollup produces far more cleaner output but doesn’t have all plugins that webpack has.

I’ve tried different config configurations, concatenateModules option, etc with no luck.