JavaScript IE/Edge Compatibility
As JavaScript evolved through ECMAScript versions (ES6/ES2015 onwards), browser support has varied significantly. Microsoft’s Internet Explorer (IE) has historically lagged behind, while Microsoft Edge has progressively aligned with modern standards. Understanding compatibility is critical for developers maintaining legacy applications or targeting enterprise environments.
Internet Explorer (IE) Compatibility
Last Major Version: IE11 (2013)
JavaScript Engine: Chakra (pre-EdgeHTML), primarily ES5 with limited ES6 support.
Status: Fully deprecated for general use as of June 15, 2022. Extended security updates continue for enterprise users until 2029.
Market Share: ~0.5% globally (mostly legacy enterprise systems).
Key Limitations for ES6+ Features:
let/const→ Not supported, Babel transpilation required.- Arrow functions → Syntax errors in IE11.
- Promises → Not native; requires polyfills (core-js or es6-promise).
- async/await → Unsupported; must transpile to generator functions or Promise chains.
- Classes & custom errors → Syntax not supported; requires transpilation.
- Optional chaining (?.) and Error.cause → Not available; Babel polyfill required.
Error Handling: Only basic try-catch-finally and throw work natively. Modern async error handling via Promises or async/await is unsupported without polyfills.
Enterprise Workarounds:
- Polyfills: Add missing JS features for IE11.
- Transpilers: Convert modern JS (ES6+) to ES5 using Babel.
- IE Mode in Edge: Run legacy web applications using Microsoft Edge’s IE Mode.
Microsoft Edge Compatibility
Legacy Edge (EdgeHTML, 2015–2019):
- Partial ES6 support.
- Limited Promises and async capabilities.
Chromium-based Edge (2020+):
- Full ES6+ support, including Promises, async/await, optional chaining, and Error.cause.
- Supports all modern ECMAScript features on par with Chrome.
- Default Windows browser; regularly updated every ~6 weeks.
Advantages: Modern Edge eliminates most cross-browser compatibility issues, enabling full use of ES6+ features and advanced error-handling mechanisms.
Key ES6+ JavaScript Features and Compatibility
| Feature | Description | IE11 | Legacy Edge | Chromium Edge |
|---|---|---|---|---|
let / const | Block-scoped variables | None | Partial | Full |
| Arrow Functions | Concise function syntax | None | Partial | Full |
| Classes / Custom Errors | ES6 class syntax for inheritance and custom errors | None | Partial | Full |
| Promises | Async error handling with .catch() | Polyfill | Full | Full |
| async/await | Synchronous-like async code | Polyfill via transpile | Full | Full |
| Optional Chaining (?.) | Safe property access | None | None | Full |
| Error.cause | Nested error tracking | None | None | Full |
| Promise.finally | Cleanup after async operations | Polyfill | Partial | Full |
Sources: MDN, CanIUse, Microsoft Docs, Stack Overflow, LambdaTest.
Internet Explorer Retirement Timeline
Microsoft has officially ended support for Internet Explorer, gradually phasing it out across services:
- August 17, 2020: IE retirement announcement.
- November 30, 2020: MS Teams ended IE11 support.
- December 31, 2020: Azure DevOps Services stopped supporting IE11.
- March 31, 2021: Azure Portal ends support.
- August 17, 2021: Office 365, OneDrive, Outlook ended IE11 support.
- June 15, 2022: All general support for IE11 officially ended.
Earlier Announcements:
- Windows 11 disables IE; replaced by Edge.
- Windows 10 “replaces” IE with Edge.
- Edge Legacy (EdgeHTML/Chakra) support ended March 9, 2021; replaced by Chromium-based Edge.
Legacy Use Cases:
- Some legacy systems and old Windows OS versions still include IE11.
- Older enterprise applications rely on ActiveX components or AJAX-based IE-specific APIs.
Solution: Microsoft Edge IE Mode allows running legacy web apps in a modern browser while maintaining compatibility.