Online/offline status

- LS

Events to indicate when the user's connected (online and offline events) and the navigator.onLine property to see current status.

IE

  1. 5.5 - 7: Not supported
  2. 8: Partial support
  3. 9 - 10: Supported
  4. 11: Supported

Edge

  1. 12 - 85: Supported
  2. 86: Supported

Firefox

  1. 2 - 3: Not supported
  2. 3.5 - 3.6: Supported
  3. 4 - 40: Partial support
  4. 41 - 80: Supported
  5. 81: Supported
  6. 82 - 83: Supported

Chrome

  1. 4 - 13: Not supported
  2. 14 - 85: Supported
  3. 86: Supported
  4. 87 - 89: Supported

Safari

  1. 3.1 - 4: Not supported
  2. 5 - 13.1: Supported
  3. 14: Supported
  4. TP: Supported

Opera

  1. 9 - 12: Not supported
  2. 12.1: Partial support
  3. 15 - 70: Supported
  4. 71: Supported

iOS Safari

  1. 3.2 - 4.1: Support unknown
  2. 4.2 - 13.7: Supported
  3. 14: Supported

Opera Mini

  1. all: Not supported

Android Browser

  1. 2.1 - 2.2: Support unknown
  2. 2.3 - 4.4.4: Supported
  3. 81: Supported

Blackberry Browser

  1. 7: Partial support
  2. 10: Supported

Opera Mobile

  1. 10 - 12.1: Not supported
  2. 59: Supported

Chrome for Android

  1. 85: Supported

Firefox for Android

  1. 79: Supported

IE Mobile

  1. 10: Supported
  2. 11: Supported

UC Browser for Android

  1. 12.12: Supported

Samsung Internet

  1. 4 - 11.2: Supported
  2. 12.0: Supported

QQ Browser

  1. 10.4: Supported

Baidu Browser

  1. 7.12: Supported

KaiOS Browser

  1. 2.5: Supported

"online" does not always mean connection to the internet, it can also just mean connection to some network.

Early versions of Chrome and Safari always reported "true" for navigator.onLine

Resources:
MDN Web Docs - NavigatorOnLine.onLine