Polyfill and standard API can provide the same functionality for older browsers. For example, you want IE browser realize Promise and fetch function, you need to manually introduced es6-promise, whatwg-fetch. And by Polyfill.io, you only need to introduce a JS file.
<script src="https://cdn.polyfill.io/v2/polyfill.min.js"></script>
Polyfill.io request header by analyzing information UserAgent automatically load the required browser polyfills. Polyfill.io have a default list of features, including the most common polyfills: document.querySelector, Element.classList, ES5 new Array methods, Date.now, ES6 in Object.assign, Promise and so on.
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> <script src="https://cdn.polyfill.io/v2/polyfill.min.js?callback=main" async defer></script> <script> function main(){ var node=document.createElement("script"); node.src="index.js"; document.body.appendChild(node); } </script> </head> <body> </body> </html>
Reference link: https: //www.jianshu.com/p/3e0bf9a414e3