Window API: `beforeunload` event: Activation by setting `event.returnValue` to any truthy value

IE

  1. 6 - 8: Not supported
  2. 9 - 10: Supported
  3. 11: Supported

Edge

  1. 12 - 18: Not supported
  2. 79 - 118: Partial support
  3. 119 - 130: Supported
  4. 131: Supported

Firefox

  1. 2 - 5: Not supported
  2. 6 - 132: Supported
  3. 133: Supported
  4. 134 - 136: Supported

Chrome

  1. 4 - 29: Not supported
  2. 30 - 118: Partial support
  3. 119 - 130: Supported
  4. 131: Supported
  5. 132 - 134: Supported

Safari

  1. 3.1 - 7.1: Not supported
  2. 8 - 18.0: Supported
  3. 18.1: Supported
  4. 18.2 - TP: Supported

Opera

  1. 10 - 16: Not supported
  2. 17 - 104: Partial support
  3. 105 - 113: Supported
  4. 114: Supported

Safari on iOS

  1. 3.2 - 18.0: Not supported
  2. 18.1: Not supported
  3. 18.2: Not supported

Opera Mini

  1. all: Support unknown

Android Browser

  1. 2.1 - 4.3: Not supported
  2. 4.4 - 4.4.4: Partial support
  3. 131: Supported

Opera Mobile

  1. 12 - 12.1: Not supported
  2. 80: Supported

Chrome for Android

  1. 131: Supported

Firefox for Android

  1. 132: Supported

UC Browser for Android

  1. 15.5: Support unknown

Samsung Internet

  1. 4 - 24: Partial support
  2. 25: Supported
  3. 26: Supported

QQ Browser

  1. 14.9: Support unknown

Baidu Browser

  1. 13.52: Support unknown

KaiOS Browser

  1. 2.5: Support unknown
  2. 3: Support unknown