The loader configuration in the configuration file
can be matched according to the configuration file Go to the rule and execute the corresponding loader.
// analyze.config.js // 引入loader const jsLoader = require('./lib/jsLoader') const jsonLoader = require('./lib/jsonLoader') const cssLoader = require('./lib/cssLoader') const htmlLoader = require('./lib/htmlLoader') const signLoader = require('./lib/signLoader') const config = { entry: './', output: { name: 'dist', src: './' }, module: [ { test: /\.js$/, loader: [signLoader, jsLoader], }, { test: /\.wxss$/, loader: [cssLoader], outputPath: (outputPath) => outputPath.replace('.wxss', '.acss') }, { test: /\.wxml$/, loader: [htmlLoader], outputPath: (outputPath) => outputPath.replace('.wxml', '.axml') }, { test: /\.json$/, loader: [jsonLoader], }, ] } module.exports = config
Specific loader implementation
Take jsLoader as an example, receive the source code as a parameter, and return the new source code obtained after compilation
// 前几篇中封装的js转换器 const JsParser = require('./JsParser') function loader(source) { const jsParser = new JsParser() let ast = jsParser.parse(source) ast = jsParser.astConverter(ast) return jsParser.astToCode(ast) } module.exports = loader
Different file selections Corresponding to loader
// 重写Analyze函数中的analyzeFileToLoard文件分析部分 function Analyze(filePath, outputPath){ if (fs.statSync(filePath).isDirectory()) { const files = fs.readdirSync(filePath) files.forEach(file => { const currentFilePath = filePath+'/'+file const currentOutputPath = outputPath+'/'+file if(fs.statSync(currentFilePath).isDirectory()) { fs.mkdirSync(currentOutputPath) Analyze(currentFilePath, currentOutputPath) } else analyzeFileToLoard(currentFilePath, currentOutputPath) }) } else analyzeFileToLoard(filePath, outputPath) }
function analyzeFileToLoard(inputPath, outputPath) { let source = readFile(inputPath) // 读取源码 const loaders = config.module loaders.forEach(loader => { // 遍历配置文件,看是否有匹配文件的loader规则 if (loader.test.test(inputPath)) { // 使用loader source = useLoader(source, loader.loader, outputPath) // 输出路径处理函数 if (loader.outputPath) outputPath = loader.outputPath(outputPath) } }) writeFile(outputAppPath(outputPath), source) // 将处理过后的源码写入文件 }
loader filtering and execution
loader execution is in reverse order, executed from right to left. Here we first use the synchronous loader to discuss.
There is a pitch stage before the loader is executed. I feel that the naming method of pitch is not particularly suitable. I prefer to call it the filtering stage. First, execute the pitch method on the loader sequentially. If the pitch has a return value, the loader executed before the loader will no longer be executed.
function useLoader(source, loaders = []) { // 执行loader存储列表 const loaderList = [] // 递归去筛选需要执行的loader function loaderFilter(loaders) { const [firstLoader, ...ortherLoader] = loaders if (loaders.length === 0) return // 执行pitch,并将剩余的loader传入作为参数 if (firstLoader.pitch && firstLoader.pitch(ortherLoader)) return ortherLoader else { // 将可用loader加入待执行列表 loaderList.push(firstLoader) // 剩余loader作为参数 递归调用 loaderFilter(ortherLoader) } } // 大概,暂时用不到。。。 const remainLoader = loaderFilter(loaders) // 同步loader逆序执行 function runLoader(source, loaderList) { const loader = loaderList.pop() let newSource = loader(source) if (loaderList.length > 0) return runLoader(newSource, loaderList) else return newSource } source = runLoader(source, loaderList) return source }
Experiment
Write a signLoader to see if the loader can be executed in reverse order as we thought
function loader(source) { let sign = `/** * @Author: LY */ ` source = sign + source return source } module.exports = loader
Result:
It’s so simple The loader part is considered completed, but writing this way can only execute some synchronous loaders, and asynchronous loaders cannot wait for execution to complete before writing.
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