babel-polyfillのArrayの処理まわりがやっていること

index.js

// 元のこんなコードを読み解く
//
// let DEFINE_PROPERTY = "defineProperty";
// function define(O, key, value) {
//   O[key] || Object[DEFINE_PROPERTY](O, key, {
//     writable:     true,
//     configurable: true,
//     value:        value
//   });
// }
// 
// "pop,reverse,shift,keys,values,entries,indexOf,every,some,forEach,map,filter,find,findIndex,includes,join,slice,concat,push,splice,unshift,sort,lastIndexOf,reduce,reduceRight,copyWithin,fill".split(",").forEach(function(key) {
//   [][key] && define(Array, key, Function.call.bind([][key]));
// });

console.log([].pop) // [Function: pop]
console.log(Array.pop) // undefined

///////////////
const target = []
if(!target["pop"]){
  return
}
if(Array["pop"]){
  return
}

Object.defineProperty(Array, "pop", {
  writable:     true,
  configurable: true,
  value:        Function.call.bind(target["pop"])
});
///////////////

console.log([].pop) // [Function: pop]
console.log(Array.pop) // [Function: bound call]