isIE

1/**
2 * Detects if the current browser is Internet Explorer.
3 *
4 * Checks for legacy `document.documentMode` (IE 6–11).
5 *
6 * @returns True if Internet Explorer is detected.
7 */
8export function isIE(): boolean {
9  if (typeof window === 'undefined') return false;
10  return !!(document as any).documentMode;
11}

• Reliable Detection Method

  Uses document.documentMode, a well-known and dependable property unique to Internet Explorer versions 6 through 11.

• Safe for Non-Browser Environments

  Includes a guard clause to avoid errors in server-side rendering or non-browser runtimes.

• Lightweight and Fast

  Executes a simple boolean check with negligible performance impact.

Tests | Examples

1const originalDocumentMode = (document as any).documentMode;
2
3afterEach(() => {
4  (document as any).documentMode = originalDocumentMode;
5});
6
7test('returns true if documentMode is present (IE)', () => {
8  (document as any).documentMode = 11;
9  expect(isIE()).toBe(true);
10});
11
12test('returns false if documentMode is undefined (not IE)', () => {
13  delete (document as any).documentMode;
14  expect(isIE()).toBe(false);
15});

Common Use Cases

• Displaying Deprecation Notices

  Inform users that IE is no longer supported and recommend modern browsers.

• Conditional Polyfill Loading

  Dynamically load scripts to patch missing features when IE is detected.

• Graceful Degradation

  Disable or simplify advanced features that won’t work properly in IE.

• Analytics and Logging

  Track usage of unsupported browsers for business or technical insights.