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next.js/build/webpack/plugins/nextjs-ssr-module-cache.js

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import webpack from 'webpack'
import { RawSource } from 'webpack-sources'
import { join, relative, dirname } from 'path'
const SSR_MODULE_CACHE_FILENAME = 'ssr-module-cache.js'
// By default webpack keeps initialized modules per-module.
// This means that if you have 2 entrypoints loaded into the same app
// they will *not* share the same instance
// This creates many issues when developers / libraries rely on the singleton pattern
// As this pattern assumes every module will have 1 instance
// This plugin overrides webpack's code generation step to replace `installedModules`
// The replacement is a require for a file that's also generated here that only exports an empty object
// Because of Node.js's single instance modules this makes webpack share all initialized instances
// Do note that this module is only geared towards the `node` compilation target.
// For the client side compilation we use `runtimeChunk: 'single'`
export default class NextJsSsrImportPlugin {
constructor (options) {
this.options = options
}
apply (compiler) {
const {outputPath} = this.options
compiler.hooks.emit.tapAsync('NextJsSSRModuleCache', (compilation, callback) => {
compilation.assets[SSR_MODULE_CACHE_FILENAME] = new RawSource(`
/* This cache is used by webpack for instantiated modules */
module.exports = {}
`)
callback()
})
compiler.hooks.compilation.tap('NextJsSSRModuleCache', (compilation) => {
compilation.mainTemplate.hooks.localVars.intercept({
register (tapInfo) {
if (tapInfo.name === 'MainTemplate') {
tapInfo.fn = (source, chunk) => {
const pagePath = join(outputPath, dirname(chunk.name))
const relativePathToBaseDir = relative(pagePath, join(outputPath, SSR_MODULE_CACHE_FILENAME))
// Make sure even in windows, the path looks like in unix
// Node.js require system will convert it accordingly
const relativePathToBaseDirNormalized = relativePathToBaseDir.replace(/\\/g, '/')
return webpack.Template.asString([
source,
'// The module cache',
`var installedModules = require('${relativePathToBaseDirNormalized}');`
])
}
}
return tapInfo
}
})
})
}
}