KeyboardEvent.key

- WD

A KeyboardEvent property whose value is a string identifying the key that was pressed. Covers character keys, non-character keys (e.g. arrow keys), and dead keys.

IE

  1. 5.5 - 8
  2. 9 - 10
  3. 11

Edge

  1. 12 - 18
  2. 79 - 81
  3. 83

Firefox

  1. 2 - 22
  2. 23 - 28
  3. 29 - 75
  4. 76
  5. 77 - 78

Chrome

  1. 4 - 50
  2. 51 - 81
  3. 83
  4. 84 - 86

Safari

  1. 3.1 - 10
  2. 10.1 - 13
  3. 13.1
  4. TP

Opera

  1. 9 - 11.6
  2. 12
  3. 12.1
  4. 15 - 37
  5. 38 - 67
  6. 68

iOS Safari

  1. 3.2 - 10.2
  2. 10.3 - 13.3
  3. 13.4

Opera Mini

  1. all

Android Browser

  1. 2.1 - 4.4.4
  2. 81

Blackberry Browser

  1. 7
  2. 10

Opera Mobile

  1. 10 - 11.5
  2. 12
  3. 12.1
  4. 46

Chrome for Android

  1. 81

Firefox for Android

  1. 68

IE Mobile

  1. 10
  2. 11

UC Browser for Android

  1. 12.12

Samsung Internet

  1. 4
  2. 5 - 10.1
  3. 11.1

QQ Browser

  1. 10.4

Baidu Browser

  1. 7.12

KaiOS Browser

  1. 2.5

"Some key events, or their values, might be suppressed by the IME in use". On mobile (virtual keyboard), for every key Blink and WebKit based browsers report "Unidentified", Gecko reports "Process".

Resources:
WebKit feature request bug
Chrome tracking bug
Edge bug report
MDN Web Docs - key
shim-keyboard-event-key: shim for non-standard key identifiers for IE & Edge
Spec listing all key string values