MinifyJSONWebpackPlugin: -

No need loaders, just add plugin after all plugins, and he minify all json assets which find. If some plugin generates a json file, then my plugin will also find this file and compress =)

const MinifyJSONWebpackPlugin = require('minify-json-webpack-plugin')

webpackConfig = {
  plugins: [
    new MinifyJSONWebpackPlugin()
  ]
}

Features: -

Minify all json files which find
No need loaders
Can be used to generate translation dictionaries, manifest.json, and for anything else, any file with the json extension will be minified.

Requires:

Webpack ^4.0.0

Plugin code:

(Yes, that's all)

class MinifyJSONWebpackPlugin {

  apply(compiler) {
    compiler.hooks.emit.tap(this.constructor.name, ({assets}) => {
      for (let filename in assets) {
        if (!assets.hasOwnProperty(filename)) continue
        if (!/\.json$/.test(filename)) continue
        const json = assets[filename].source().toString()
        const jsonMinified = JSON.stringify(JSON.parse(json)) // magic minify =)
        assets[filename] = new RawSource(jsonMinified)
      }
    })
  }

}

Package detail

minify-json-webpack-plugin

readme

Plugin code: