Element: underflow event

This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

The non-standard underflow event, which is specific to Firefox, is fired when an element is no longer overflowed by its content. This only works for elements for which overflow is not set to visible.

The counterpart overflow event is fired when overflow occurs.

Bubbles Yes
Cancelable Yes
Interface UIEvent
Event handler property Unknown


<div id="wrapper">
    <div id="child"></div>
<label><input type="checkbox" id="toggle" checked/> Overflow</label>

 #wrapper {
    width: 20px;
    height: 20px;
    background: #000;
    padding: 5px;
    overflow: hidden;

  #child {
    width: 40px;
    height: 40px;
    border: 2px solid grey;
    background: #ccc;

  var wrapper = document.getElementById("wrapper"),
      child = document.getElementById("child"),
      toggle = document.getElementById("toggle");

  wrapper.addEventListener("overflow", function( event ) {
      console.log( event );
  }, false);

  wrapper.addEventListener("underflow", function( event ) {
      console.log( event );
  }, false);

  toggle.addEventListener("change", function( event ) {
      if ( event.target.checked ) {
          child.style.width = "40px";
          child.style.height = "40px";
      } else {
          child.style.width = "10px";
          child.style.height = "10px";
  }, false);


Not part of any specification.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
underflow event
Chrome No support NoEdge No support NoFirefox Full support YesIE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoFirefox Android Full support YesOpera Android No support NoSafari iOS No support NoSamsung Internet Android No support No


Full support  
Full support
No support  
No support
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.

See also