{
  vue: '/path/to/your/project/node_modules/vue/dist/vue.runtime.esm-bundler.js',
  'element-plus': '/path/to/your/project/node_modules/element-plus/es/index.mjs',
  'vue-router': '/path/to/your/project/node_modules/vue-router/dist/vue-router.esm-bundler.js'
}

//...省略其他代碼
  if (explicitEntryPatterns) {
    entries = await globEntries(explicitEntryPatterns, config)
  } else if (buildInput) {
    const resolvePath = (p: string) => path.resolve(config.root, p)
    if (typeof buildInput === 'string') {
      entries = [resolvePath(buildInput)]
    } else if (Array.isArray(buildInput)) {
      entries = buildInput.map(resolvePath)
    } else if (isObject(buildInput)) {
      entries = Object.values(buildInput).map(resolvePath)
    } else {
      throw new Error('invalid rollupOptions.input value.')
    }
  } else {
    // 重點(diǎn)看這里：使用html文件作為查找入口
    entries = await globEntries('**/*.html', config)
  }
//...省略其他代碼
build.onResolve(
        {
          // avoid matching windows volume
          filter: /^[\w@][^:]/
        },
        async ({ path: id, importer }) => {
          const resolved = await resolve(id, importer)
          if (resolved) {
            // 來自node_modules和在include中指定的模塊
            if (resolved.includes('node_modules') || include?.includes(id)) {
              // dependency or forced included, externalize and stop crawling
              if (isOptimizable(resolved)) {
                // 重點(diǎn)看這里：將符合預(yù)構(gòu)建條件的依賴記錄下來，depImports就是對外導(dǎo)出的需要預(yù)構(gòu)建的依賴對象
                depImports[id] = resolved
              }
              return externalUnlessEntry({ path: id })
            } else if (isScannable(resolved)) {
              const namespace = htmlTypesRE.test(resolved) ? 'html' : undefined
              // linked package, keep crawling
              return {
                path: path.resolve(resolved),
                namespace
              }
            } else {
              return externalUnlessEntry({ path: id })
            }
          } else {
            missing[id] = normalizePath(importer)
          }
        }
      )

      // 對于html類型(.VUE/.HTML/.svelte等)的文件，提取文件里的script內(nèi)容。html types: extract script contents -----------------------------------
      build.onResolve({ filter: htmlTypesRE }, async ({ path, importer }) => {
        const resolved = await resolve(path, importer)
        if (!resolved) return
        // It is possible for the scanner to scan html types in node_modules.
        // If we can optimize this html type, skip it so it's handled by the
        // bare import resolve, and recorded as optimization dep.
        if (resolved.includes('node_modules') && isOptimizable(resolved)) return
        return {
          path: resolved,
          namespace: 'html'
        }
      })
      // 配合build.onResolve，對于類html文件，提取其中的script，作為一個(gè)js模塊extract scripts inside HTML-like files and treat it as a js module
      build.onLoad(
        { filter: htmlTypesRE, namespace: 'html' },
        async ({ path }) => {
          let raw = fs.readFileSync(path, 'utf-8')
          // Avoid matching the content of the comment
          raw = raw.replace(commentRE, '<!---->')
          const isHtml = path.endsWith('.html')
          const regex = isHtml ? scriptModuleRE : scriptRE
          regex.lastIndex = 0
          // js 的內(nèi)容被處理成了一個(gè)虛擬模塊
          let js = ''
          let scriptId = 0
          let match: RegExpExecArray | null
          while ((match = regex.exec(raw))) {
            const [, openTag, content] = match
            const typeMatch = openTag.match(typeRE)
            const type =
              typeMatch && (typeMatch[1] || typeMatch[2] || typeMatch[3])
            const langMatch = openTag.match(langRE)
            const lang =
              langMatch && (langMatch[1] || langMatch[2] || langMatch[3])
            // skip type="application/ld+json" and other non-JS types
            if (
              type &&
              !(
                type.includes('javascript') ||
                type.includes('ecmascript') ||
                type === 'module'
              )
            ) {
              continue
            }
            // 默認(rèn)的js文件的loader是js，其他對于ts、tsx jsx有對應(yīng)的同名loader
            let loader: Loader = 'js'
            if (lang === 'ts' || lang === 'tsx' || lang === 'jsx') {
              loader = lang
            }
            const srcMatch = openTag.match(srcRE)
            // 對于<script src='path/to/some.js'>引入的js，將它轉(zhuǎn)換為import 'path/to/some.js'的代碼
            if (srcMatch) {
              const src = srcMatch[1] || srcMatch[2] || srcMatch[3]
              js += `import ${JSON.stringify(src)}\n`
            } else if (content.trim()) {
              // The reason why virtual modules are needed:
              // 1. There can be module scripts (`<script context="module">` in Svelte and `<script>` in Vue)
              // or local scripts (`<script>` in Svelte and `<script setup>` in Vue)
              // 2. There can be multiple module scripts in html
              // We need to handle these separately in case variable names are reused between them
              // append imports in TS to prevent esbuild from removing them
              // since they may be used in the template
              const contents =
                content +
                (loader.startsWith('ts') ? extractImportPaths(content) : '')
                // 將提取出來的script腳本，存在以xx.vue?id=1為key的script對象中script={'xx.vue?id=1': 'js contents'}
              const key = `${path}?id=${scriptId++}`
              if (contents.includes('import.meta.glob')) {
                scripts[key] = {
                  // transformGlob already transforms to js
                  loader: 'js',
                  contents: await transformGlob(
                    contents,
                    path,
                    config.root,
                    loader,
                    resolve,
                    config.logger
                  )
                }
              } else {
                scripts[key] = {
                  loader,
                  contents
                }
              }
              const virtualModulePath = JSON.stringify(
                virtualModulePrefix + key
              )
              const contextMatch = openTag.match(contextRE)
              const context =
                contextMatch &&
                (contextMatch[1] || contextMatch[2] || contextMatch[3])
              // Especially for Svelte files, exports in <script context="module"> means module exports,
              // exports in <script> means component props. To avoid having two same export name from the
              // star exports, we need to ignore exports in <script>
              if (path.endsWith('.svelte') && context !== 'module') {
                js += `import ${virtualModulePath}\n`
              } else {
                // e.g. export * from 'virtual-module:xx.vue?id=1'
                js += `export * from ${virtualModulePath}\n`
              }
            }
          }
          // This will trigger incorrectly if `export default` is contained
          // anywhere in a string. Svelte and Astro files can't have
          // `export default` as code so we know if it's encountered it's a
          // false positive (e.g. contained in a string)
          if (!path.endsWith('.vue') || !js.includes('export default')) {
            js += '\nexport default {}'
          }
          return {
            loader: 'js',
            contents: js
          }
        }
      )

//使用esbuild打包，入口文件即為第一步中抓取到的需要預(yù)構(gòu)建的依賴
    import { build } from 'esbuild'
   // ...省略其他代碼
    const result = await build({
      absWorkingDir: process.cwd(),
     // flatIdDeps即為第一步中所得到的需要預(yù)構(gòu)建的依賴對象
      entryPoints: Object.keys(flatIdDeps),
      bundle: true,
      format: 'esm',
      target: config.build.target || undefined,
      external: config.optimizeDeps?.exclude,
      logLevel: 'error',
      splitting: true,
      sourcemap: true,
// outdir指定打包產(chǎn)物輸出目錄，processingCacheDir這里并不是.vite，而是存放構(gòu)建產(chǎn)物的臨時(shí)目錄
      outdir: processingCacheDir,
      ignoreAnnotations: true,
      metafile: true,
      define,
      plugins: [
        ...plugins,
        esbuildDepPlugin(flatIdDeps, flatIdToExports, config, ssr)
      ],
      ...esbuildOptions
    })
    // 寫入_metadata文件，并替換緩存文件。Write metadata file, delete `deps` folder and rename the new `processing` folder to `deps` in sync
    commitProcessingDepsCacheSync()

  function commitProcessingDepsCacheSync() {
    // Rewire the file paths from the temporal processing dir to the final deps cache dir
    const dataPath = path.join(processingCacheDir, '_metadata.json')
    writeFile(dataPath, stringifyOptimizedDepsMetadata(metadata))
    // Processing is done, we can now replace the depsCacheDir with processingCacheDir
    // 依賴處理完成后，使用依賴緩存目錄替換處理中的依賴緩存目錄
    if (fs.existsSync(depsCacheDir)) {
      const rmSync = fs.rmSync ?? fs.rmdirSync // TODO: Remove after support for Node 12 is dropped
      rmSync(depsCacheDir, { recursive: true })
    }
    fs.renameSync(processingCacheDir, depsCacheDir)
  }
}

{
  "hash": "22135fca",
  "browserHash": "632454bc",
  "optimized": {
    "vue": {
      "file": "/path/to/your/project/node_modules/.vite/vue.js",
      "src": "/path/to/your/project/node_modules/vue/dist/vue.runtime.esm-bundler.js",
      "needsInterop": false
    },
    "element-plus": {
      "file": "/path/to/your/project/node_modules/.vite/element-plus.js",
      "src": "/path/to/your/project/node_modules/element-plus/es/index.mjs",
      "needsInterop": false
    },
    "vue-router": {
      "file": "/path/to/your/project/node_modules/.vite/vue-router.js",
      "src": "/path/to/your/project/node_modules/vue-router/dist/vue-router.esm-bundler.js",
      "needsInterop": false
    }
  }
}

// 基于配置文件+依賴信息生成hash
const lockfileFormats = ['package-lock.json', 'yarn.lock', 'pnpm-lock.yaml']
function getDepHash(root: string, config: ResolvedConfig): string {
  let content = lookupFile(root, lockfileFormats) || ''
  // also take config into account
  // only a subset of config options that can affect dep optimization
  content += JSON.stringify(
    {
      mode: config.mode,
      root: config.root,
      define: config.define,
      resolve: config.resolve,
      buildTarget: config.build.target,
      assetsInclude: config.assetsInclude,
      plugins: config.plugins.map((p) => p.name),
      optimizeDeps: {
        include: config.optimizeDeps?.include,
        exclude: config.optimizeDeps?.exclude,
        esbuildOptions: {
          ...config.optimizeDeps?.esbuildOptions,
          plugins: config.optimizeDeps?.esbuildOptions?.plugins?.map(
            (p) => p.name
          )
        }
      }
    },
    (_, value) => {
      if (typeof value === 'function' || value instanceof RegExp) {
        return value.toString()
      }
      return value
    }
  )
  return createHash('sha256').update(content).digest('hex').substring(0, 8)
}

// 計(jì)算當(dāng)前的hash
const mainHash = getDepHash(root, config)
 const metadata: DepOptimizationMetadata = {
    hash: mainHash,
    browserHash: mainHash,
    optimized: {},
    discovered: {},
    processing: processing.promise
  }
 let prevData: DepOptimizationMetadata | undefined
    try {
      const prevDataPath = path.join(depsCacheDir, '_metadata.json')
      prevData = parseOptimizedDepsMetadata(
        fs.readFileSync(prevDataPath, 'utf-8'),
        depsCacheDir,
        processing.promise
      )
    } catch (e) { }
    // hash is consistent, no need to re-bundle
    // 比較緩存的hash與當(dāng)前hash
    if (prevData && prevData.hash === metadata.hash) {
      log('Hash is consistent. Skipping. Use --force to override.')
      return {
        metadata: prevData,
        run: () => (processing.resolve(), processing.promise)
      }
    }