GlobalEventHandlers.onwheel

The onwheel property of the GlobalEventHandlers mixin is an EventHandler that processes wheel events.

The wheel event fires when the user rotates the mouse (or other pointing device) wheel.

target.onwheel = functionRef;

functionRef is a function name or a function expression. The function receives a WheelEvent object as its sole argument.

This example shows how to scale an element using the mouse (or other pointing device) wheel.

<div>Scale me with your mouse wheel.</div>

body {
  min-height: 100vh;
  margin: 0;
  display: flex;
  align-items: center;
  justify-content: center;
}

div {
  width: 80px;
  height: 80px;
  background: #cdf;
  padding: 5px;
  transition: transform .3s;
}

function zoom(event) {
  event.preventDefault();

  if (event.deltaY < 0) {
    // Zoom in
    scale *= event.deltaY * -2;
  }
  else {
    // Zoom out
    scale /= event.deltaY * 2;
  }

  // Restrict scale
  scale = Math.min(Math.max(.125, scale), 4);

  // Apply scale transform
  el.style.transform = `scale(${scale})`;
}

let scale = 1;
const el = document.querySelector('div');
document.onwheel = zoom;

• Document: wheel event
• Element: wheel event