Webpack source flow

Zhaoguang 2021-02-23 16:12:18
webpack source flow


webpack It's a static module packaging tool . When webpack When processing an application , It recursively builds a dependency graph , It contains every module the application needs , Then package these modules into one or more bundle.

Some of the core options:

  • entry entrance
  • output
  • loader
  • plugin plug-in unit
  • mode Packaging mode

webpack Implementation process reference

Overall process

Integrate option(config + shell config) --> addEntry --> addModuleChain & addModuleDependcies --> buildModule --> seal Deal with each one chunk, Merge 、 Split 、 Generate hash --> createAssets & outputAssets --> end

Key event nodes

  • entryOption stay entry After the configuration item has been processed , perform
  • watchRun In monitor mode , A new compilation (compilation) After the trigger , Execute a plug-in
  • build-module , Mainly called loader Processing source files , Generate AST, Traverse AST, encounter require\import Such dependence , Create a dependency and add it to the dependency array
  • after-compile This is in seal Stage , For each module and chunk To organize , Generate compiled source code , Merge , Split , Generate hash.
  • emit event Generate resources to output Before the catalog .
  • after-emit Generate resources to output After the catalog .

Here are a few concepts that need to be clarified :

  • compiler And compilation The difference between objects

    • compiler On behalf of the entire webpack Life cycle from Startup to shutdown
    • compilation Object represents a new compilation modules become chunks Compilation process .(modules All parsed modules are recorded ; chunks It records everything chunk; assets All the files to be generated are recorded )
  • Tapable class

Mainly controls the publication and subscription of hook functions ( Observer mode ), Controls the webpack The plug-in system ,compiler & compilation Inherit from Tapaple . Tapable Libraries expose a lot of different types of hook

const {
SyncHook,
SyncBailHook,
SyncWaterfallHook,
SyncLoopHook,
AsyncParallelHook,
AsyncParallelBailHook,
AsyncSeriesHook,
AsyncSeriesBailHook,
AsyncSeriesWaterfallHook
} = require("tapable");
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Hook Class :

  • tap(name, fn): Register callback function fn, Just the current fn The code is finished ,Hook The next one will be executed fn;
  • tapAsync(name, fn, callback): Register callback functions with asynchronous operations , By calling the input parameter callback() inform Hook At present fn Execution completed , You can execute the next fn;
  • call(...args): according to Hook All callback functions are executed according to the corresponding rules ;
  • Async: Supports asynchronous operations in callback functions , It doesn't refer to the execution rules of the callback function ;
  • Series: Indicates that the execution rule of the callback function is serial , Empathy Parallel According to the parallel ;

therefore AsyncSeriesHook, Supports asynchronous operations in callback functions , And all registered callback functions are executed serially ;

compiler The event hook of the whole process is based on tapable Of hook Of

class Compiler extends Tapable {
consturctor(context){
super()
this.hooks = {
beforeCompile: new AsyncSeriesHook(),
compile: new SyncHook(['params']),
afterCompile: xxx,
enterOption: xxx,
// ... Many types of hooks are defined
}
}
}
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With tapable Of syncHook Simple display , Here's a typical observer pattern

class SyncHook {
consturctor(){
this.hooks = []
}
// subscribe
tap(name, fn){
this.hooks.push(fn)
}
// Release
call(){
this.hooks.forEach(hook => hook(...arguments))
}
}
use
const hooks1 = new SyncHook()
hooks1.tap('hook1', ()=>{})
hooks1.tap('hook2', ()=>{})
// Synchronous execution
hooks1.call()
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Then refer to the plug-in writing , You can understand compiler.hooks.enterOption.tab 了 .

Help us in different modes , Plug in introduced

common problem :

1、 How does the packaging process relate to plug-ins ? technological process +tapable.

Briefly describe the process +tapable

2、 Package optimization ?

got it , Let's talk about packaging optimization , It's clearer

  • 1、 Narrow file search

Make good use of rules Under the exclude, You don't need to babel-loader Documents processed ;

{
rules: [{
test: /\.js$/,
use: {
loader: 'babel-loader'
},
// exclude: /node_modules/,
include: [path.resolve(__dirname, 'src')]
}]
}
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Third party libraries for references (jq,chartjs), No parsing and conversion .

 module: {
//noParse: /jquery|lodash|chartjs/,
noParse: function(content){
return /jquery|lodash|chartjs/.test(content)
}
}
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names alias , image @ @utils etc.

resolve.modules tell webpack Find references , Reduce business side ../../xx Use . such as :path.resolve(__dirname, "src")

utilize extensions The field tells webpack, The import module , Automatically bring in the suffix to try to match the corresponding file , Reduce traversal . It's best to import files in code , Try to put a suffix on it , Avoid finding .

 resolve: {
extensions: ['.js', '.json']
}
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  • 2、 Reduce packaging files

1、 Advance public code webpack 3 With CommonsChunkPlugin,webpack 4 With SplitChunksPlugin

2、 Make good use of tree-shaking, Remove useless code . It's all written in import xx from , modify babel Of preset( By default, any module type is compiled to Commonjs)

3、 Third party library leads to cdn Image formation vue、common、 Business js.

4、 Use the third-party library to find that kind of ES Module version of , Good for tree-shaking

  • 3、 cache

cache-loader Conduct loader The cache of

 {
test: /\.js/,
use: [
{
loader: 'cache-loader'
},
{
loader: "babel-loader",
},
],
}
{
test: /\.js/,
use: [
{
loader: "babel-loader",
options: {
cacheDirectory: true
}
},
],
}
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HardSourceWebpackPlugin It can also provide caching function for modules .

plugins: [
new HardSourceWebpackPlugin()
]
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  • 4、 Multi process

thread-loader happypack Realize multi process processing , The actual effect is not obvious .

3、webpack5 What's new ?

  • 1、 Persistent cache 、 Long term cache , Improve build performance .
  • 2、 Better tree-shaking, Reduce volume .
  • 3、 No more for Node.js modular Auto reference Polyfills, Reduce the volume .

Learning links :

webpack

tabable

mini-pack Simplify the example

webpack-5-release

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本文为[Zhaoguang]所创,转载请带上原文链接,感谢
https://qdmana.com/2021/02/20210223155148648Z.html

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