DOM

HTML needs this to define event handlers. [HTML]

To , given an EventTarget object eventTarget, for each listener of eventTarget’s event listener list, remove an event listener with eventTarget and listener.

HTML needs this to define document.open(). [HTML]

EventTarget/removeEventListener

In all current engines.

Firefox1+Safari1+Chrome1+ Opera7+Edge79+ Edge (Legacy)12+IE9+ Firefox for Android4+iOS Safari1+Chrome for Android18+Android WebView1+Samsung Internet1.0+Opera Mobile10.1+ Node.js14.5.0+

The method steps are:

The event listener list will not contain multiple event listeners with equal type, callback, and capture, as add an event listener prevents that.

EventTarget/dispatchEvent

In all current engines.

Firefox2+Safari3.2+Chrome4+ Opera9+Edge79+ Edge (Legacy)12+IE9+ Firefox for Android4+iOS Safari3+Chrome for Android18+Android WebView4+Samsung Internet1.0+Opera Mobile10.1+ Node.js14.5.0+

The dispatchEvent(event) method steps
are:

In general, developers do not expect the presence of an event listener to be observable.
The impact of an event listener is determined by its callback. That is, a developer
adding a no-op event listener would not expect it to have any side effects.