CustomEvent

- LS

A DOM event interface that can carry custom application-defined data.

IE

  1. 5.5 - 8: Not supported
  2. 9 - 10: Partial support
  3. 11: Partial support

Edge

  1. 12 - 89: Supported
  2. 90: Supported

Firefox

  1. 2 - 5: Not supported
  2. 6 - 10: Partial support
  3. 11 - 86: Supported
  4. 87: Supported
  5. 88 - 89: Supported

Chrome

  1. 4: Not supported
  2. 5 - 8: Support unknown
  3. 9 - 12: Partial support
  4. 13 - 14: Support unknown
  5. 15 - 89: Supported
  6. 90: Supported
  7. 91 - 93: Supported

Safari

  1. 3.1 - 4: Not supported
  2. 5: Support unknown
  3. 5.1: Partial support
  4. 6: Support unknown
  5. 6.1 - 13.1: Supported
  6. 14: Supported
  7. TP: Supported

Opera

  1. 9 - 10.6: Not supported
  2. 11 - 11.5: Partial support
  3. 11.6 - 72: Supported
  4. 73: Supported

Safari on iOS

  1. 3.2: Support unknown
  2. 4: Not supported
  3. 4.2: Support unknown
  4. 5: Partial support
  5. 6 - 13.7: Supported
  6. 14: Supported

Opera Mini

  1. all: Supported

Android Browser

  1. 2.1 - 2.3: Not supported
  2. 3 - 4.3: Partial support
  3. 4.4 - 4.4.4: Supported
  4. 89: Supported

Opera Mobile

  1. 10: Not supported
  2. 11 - 11.5: Partial support
  3. 12 - 12.1: Supported
  4. 62: Supported

Chrome for Android

  1. 89: Supported

Firefox for Android

  1. 86: Supported

UC Browser for Android

  1. 12.12: Supported

Samsung Internet

  1. 4 - 12.0: Supported
  2. 13.0: Supported

QQ Browser

  1. 10.4: Supported

Baidu Browser

  1. 7.12: Supported

KaiOS Browser

  1. 2.5: Supported

Not supported in some versions of Android's old WebKit-based WebView.

Resources:
MDN Web Docs - CustomEvent
EventListener polyfill which includes a CustomEvent polyfill
Polyfill based on the MDN snippet