? JavaScript in IE (Internet Explorer) and Edge

JavaScript works in both Internet Explorer (IE) and Microsoft Edge, but there are some important differences due to browser engines and support levels.

? 1. JavaScript in Internet Explorer (IE)

• IE uses the Trident rendering engine.

• Support for modern JavaScript (ES6+) is very limited.

• Many new features like let, const, arrow functions (=>), fetch, Promise, async/await, and others don’t work in IE11 or earlier without transpiling.

Example – ? Not supported in IE:

const greet = () => console.log("Hello"); // ES6 arrow function

To support IE, you'd need to convert this to:

var greet = function () {  console.log("Hello");};

?? IE Fix Options:

• Use polyfills (like core-js)

• Use Babel to transpile ES6+ code to ES5

• Avoid modern APIs unless you add fallbacks

? 2. JavaScript in Microsoft Edge

Edge (Legacy):

• Uses EdgeHTML engine

• Slightly better than IE11, but still limited support for modern JS

• Now deprecated

Edge (Chromium-based, current):

• Uses Chromium engine (same as Google Chrome)

• Fully supports modern JavaScript (ES6, ES7, ES8, etc.)

• Fast, secure, and compatible with most JS features and APIs

? Check Browser Compatibility

To check if a feature works in IE or Edge, use:

• MDN Web Docs – Compatibility Tables

• Can I use

? Example – Feature Detection

To check if fetch is supported:

if (window.fetch) {  fetch("https://api.example.com/data")    .then(res => res.json())    .then(data => console.log(data));} else {  // Fallback for IE  console.log("Fetch is not supported in this browser");}

? Best Practice for IE + Edge Support

• Avoid unsupported features in IE unless polyfilled

• Prefer using modern JavaScript and drop IE11 support if possible (even Microsoft recommends it)

• Use progressive enhancement techniques

Would you like a list of common JS features not supported in IE11 or how to polyfill for older browsers?