defer attribute for external scripts

- LS

The boolean defer attribute on script elements allows the external JavaScript file to run when the DOM is loaded, without delaying page load first.

IE

  1. 5.5 - 9: Partial support
  2. 10: Supported
  3. 11: Supported

Edge

  1. 12 - 84: Supported
  2. 85: Supported

Firefox

  1. 2 - 3: Not supported
  2. 3.5 - 30: Supported
  3. 31 - 79: Supported
  4. 80: Supported
  5. 81 - 82: Supported

Chrome

  1. 4 - 7: Not supported
  2. 8 - 84: Supported
  3. 85: Supported
  4. 86 - 88: Supported

Safari

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

Opera

  1. 9 - 12.1: Not supported
  2. 15 - 69: Supported
  3. 70: Supported

iOS Safari

  1. 3.2 - 4.3: Not supported
  2. 5 - 13.7: Supported
  3. 14.0: Supported

Opera Mini

  1. all: Not supported

Android Browser

  1. 2.1 - 2.3: Not supported
  2. 3 - 4.4.4: Supported
  3. 81: Supported

Blackberry Browser

  1. 7: Supported
  2. 10: Supported

Opera Mobile

  1. 10 - 12.1: Not supported
  2. 46: 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
Resources:
async vs defer attributes
MDN Web Docs - Script Attributes
has.js test
WebPlatform Docs