How we built it

Support "once" event listener option

Support adding event listeners with the "once" option set to true. When set to true, options’s once member indicates that the callback will only be invoked once after which the event listener will be removed.


It is already supported in Safari Technology Preview 7, vaguely mentioned in and in the upcoming Firefox 50.



Established standard

Status in Chromium

Enabled by default (launch bug) in:

  • Chrome for desktop release 55
  • Chrome for Android release 55
  • Chrome for iOS release 55
  • Opera release 42
  • Opera for Android release 42

Consensus & Standardization


Last updated on 2016-10-20