src/index.js

import dotenv from 'dotenv-defaults'
import fs from 'fs'

// Mostly taken from here: https://github.com/motdotla/dotenv-expand/blob/master/lib/main.js#L4
const interpolate = (env, vars) => {
  const matches = env.match(/\$([a-zA-Z0-9_]+)|\${([a-zA-Z0-9_]+)}/g) || []

  matches.forEach((match) => {
    const key = match.replace(/\$|{|}/g, '')
    let variable = vars[key] || ''
    variable = interpolate(variable, vars)
    env = env.replace(match, variable)
  })

  return env
}

const isMainThreadElectron = (target) =>
  target.startsWith('electron') && target.endsWith('main')

class Dotenv {
  /**
   * The dotenv-webpack plugin.
   * @param {Object} options - The parameters.
   * @param {String} [options.path=./.env] - The location of the environment variable.
   * @param {Boolean|String} [options.safe=false] - If false ignore safe-mode, if true load `'./.env.example'`, if a string load that file as the sample.
   * @param {Boolean} [options.systemvars=false] - If true, load system environment variables.
   * @param {Boolean} [options.silent=false] - If true, suppress warnings, if false, display warnings.
   * @param {String} [options.prefix=process.env.] - The prefix, used to denote environment variables.
   * @returns {webpack.DefinePlugin}
   */
  constructor (config = {}) {
    this.config = Object.assign({}, {
      path: './.env',
      prefix: 'process.env.'
    }, config)
  }

  apply (compiler) {
    const variables = this.gatherVariables()
    const target = compiler.options.target ?? 'web'
    const version = (compiler.webpack && compiler.webpack.version) || '4'
    const data = this.formatData({
      variables,
      target,
      version
    })
    const DefinePlugin = (compiler.webpack && compiler.webpack.DefinePlugin) || require('webpack').DefinePlugin

    new DefinePlugin(data).apply(compiler)
  }

  gatherVariables () {
    const { safe, allowEmptyValues } = this.config
    const vars = this.initializeVars()

    const { env, blueprint } = this.getEnvs()

    Object.keys(blueprint).forEach(key => {
      const value = Object.prototype.hasOwnProperty.call(vars, key) ? vars[key] : env[key]

      const isMissing = typeof value === 'undefined' || value === null ||
        (!allowEmptyValues && value === '')

      if (safe && isMissing) {
        throw new Error(`Missing environment variable: ${key}`)
      } else {
        vars[key] = value
      }
    })

    // add the leftovers
    if (safe) {
      Object.keys(env).forEach((key) => {
        if (!Object.prototype.hasOwnProperty.call(vars, key)) {
          vars[key] = env[key]
        }
      })
    }

    return vars
  }

  initializeVars () {
    return (this.config.systemvars) ? Object.assign({}, process.env) : {}
  }

  getEnvs () {
    const { path, silent, safe } = this.config

    const env = dotenv.parse(this.loadFile({
      file: path,
      silent
    }), this.getDefaults())

    let blueprint = env
    if (safe) {
      let file = `${path}.example`
      if (safe !== true) {
        file = safe
      }
      blueprint = dotenv.parse(this.loadFile({
        file,
        silent
      }))
    }

    return {
      env,
      blueprint
    }
  }

  getDefaults () {
    const { path, silent, defaults } = this.config

    if (defaults) {
      return this.loadFile({
        file: defaults === true ? `${path}.defaults` : defaults,
        silent
      })
    }

    return ''
  }

  formatData ({ variables = {}, target, version }) {
    const { expand, prefix } = this.config
    const formatted = Object.keys(variables).reduce((obj, key) => {
      const v = variables[key]
      const vKey = `${prefix}${key}`
      let vValue
      if (expand) {
        if (v.substring(0, 2) === '\\$') {
          vValue = v.substring(1)
        } else if (v.indexOf('\\$') > 0) {
          vValue = v.replace(/\\\$/g, '$')
        } else {
          vValue = interpolate(v, variables)
        }
      } else {
        vValue = v
      }

      obj[vKey] = JSON.stringify(vValue)

      return obj
    }, {})

    // We have to stub any remaining `process.env`s due to Webpack 5 not polyfilling it anymore
    // https://github.com/mrsteele/dotenv-webpack/issues/240#issuecomment-710231534
    // However, if someone targets Node or Electron `process.env` still exists, and should therefore be kept
    // https://webpack.js.org/configuration/target
    if (this.shouldStub({ target, version })) {
      // Results in `"MISSING_ENV_VAR".NAME` which is valid JS
      formatted['process.env'] = '"MISSING_ENV_VAR"'
    }

    return formatted
  }

  shouldStub ({ target: targetInput, version }) {
    if (!version.startsWith('5')) {
      return false
    }

    const targets = Array.isArray(targetInput) ? targetInput : [targetInput]

    return targets.every(
      target =>
        // If configured prefix is 'process.env'
        this.config.prefix === 'process.env.' &&
        // If we're not configured to never stub
        this.config.ignoreStub !== true &&
        // And
        (
          // We are configured to always stub
          this.config.ignoreStub === false ||
          // Or if we should according to the target
          (!target.includes('node') && !isMainThreadElectron(target))
        )
    )
  }

  /**
   * Load a file.
   * @param {String} config.file - The file to load.
   * @param {Boolean} config.silent - If true, suppress warnings, if false, display warnings.
   * @returns {Object}
   */
  loadFile ({ file, silent }) {
    try {
      return fs.readFileSync(file, 'utf8')
    } catch (err) {
      this.warn(`Failed to load ${file}.`, silent)
      return {}
    }
  }

  /**
   * Displays a console message if 'silent' is falsey
   * @param {String} msg - The message.
   * @param {Boolean} silent - If true, display the message, if false, suppress the message.
   */
  warn (msg, silent) {
    !silent && console.warn(msg)
  }
}

export default Dotenv