babel-polyfill

バベルはシンタックスの変換のみをするので、

新しいグローバル

promiseや

新しいネイティブメソッド

String.padStart

など

これらをつかうためには、babe-polyfillを使う必要がある

This will emulate a full ES2015+ environment and is intended to be used in an application rather than a library/tool.

This polyfill is automatically loaded when using babel-node.

This means you can use

new built-ins like Promise or WeakMap,

static methods like Array.from or Object.assign,

instance methods like Array.prototype.includes,

and generator functions (provided you use the regenerator plugin).

The polyfill adds to the global scope as well as native prototypes like String in order to do this.