index.js

const path = require('path')
const chalk = require('chalk')

const defaultJsonOptions = {
  replacer: null,
  space: 2
}

function GenerateJsonFromJsPlugin (config = {}) {
  Object.assign(this, {
    ...config,
    filePath: config.path,
    filename: config.filename,
    data: config.data || [],
    options: {
      ...defaultJsonOptions,
      ...config.options
    }
  })

  this.plugin = 'GenerateJsonFromJsPlugin'
}

GenerateJsonFromJsPlugin.prototype.apply = function apply (compiler) {
  const emit = (compilation, callback) => {
    const fullFilePath = path.resolve(compiler.context, this.filePath)

    // Adding this causes a "rebuild" when the template file changes and indicate when the file has changed
    compilation.fileDependencies.add(fullFilePath)
    process.stdout.write(`\n${chalk.green('Rebuilding ')}${this.filename}\n`)

    const jsModule = require(fullFilePath)
    let jsonValue = null

    if (typeof jsModule === 'function') {
      jsonValue = jsModule(this.data)
    } else if (jsModule instanceof Array) {
      jsonValue = [
        ...jsModule,
        ...this.data,
      ]
    } else if (typeof jsModule === 'object') {
      jsonValue = {
        ...jsModule,
        ...this.data
      }
    }

    if (jsonValue) {
      const json = JSON.stringify(jsonValue, this.options.replacer, this.options.space)

      compilation.assets[this.filename] = {
        source: () => json,
        size: () => json.length
      }
    }

    callback()
  }

  if (compiler.hooks) {
    compiler.hooks.emit.tapAsync(this.plugin, emit)
  } else {
    compiler.plugin('emit', emit)
  }
}

module.exports = GenerateJsonFromJsPlugin