bundle-tricks

bundle.js

// .babelrc
{
  "presets": [
    [
      "@babel/preset-env",
      { 
        // this tells @babel "hey, don'y change any of the modules, let Webpack handle it
        "modules": false
         // you only get the individual pollyfill that you need
         "useBuiltIns": "usage"
      }
    ],
  ],
}

// "useBuiltIns": "usage"
  
// a.js 
var a = new Promise();
  
// b.js
var b = new Map();

// Out (if environment doesn't support it)

import "core-js/modules/es.promise";
var a = new Promise();
//
import "core-js/modules/es.map";
var b = new Map();

// Out (if environment supports it)

var a = new Promise();

var b = new Map();