Javascript WheelEvent Tutorial
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WheelEvent is an interface representing for the events occurring when an user moves mouse wheel or similar equipment.
Browsers which support WheelEvent:
WheelEvent means sub-interface of MouseEvent. It will inherit all properties and methods of parent interface.
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| Event | Description |
|---|---|
| wheel | The event occurs when the mouse wheel rolls up or down over an element |
The properties of WheelEvent:
| Property | Description |
|---|---|
| deltaX | Returns the horizontal scroll amount of a mouse wheel (x-axis) |
| deltaY | Returns the vertical scroll amount of a mouse wheel (y-axis) |
| deltaZ | Returns the scroll amount of a mouse wheel for the z-axis |
| deltaMode | Returns a number that represents the unit of measurements for delta values (DOM_DELTA_PIXEL, DOM_DELTA_PIXEL, DOM_DELTA_PAGE) |
Constants:
| Constant | Value | Description |
| DOM_DELTA_PIXEL | 0 | Measuring unit of delta is pixels. |
| DOM_DELTA_LINE | 1 | Measuring unit of delta is lines. |
| DOM_DELTA_PAGE | 2 | Measuring unit of delta is pages. |
Example with WheelEvent:
wheelevents-example.html
<!DOCTYPE html>
<html>
<head>
<title>WheelEvent Example</title>
<script src="wheelevents-example.js"></script>
</head>
<body>
<h3>WheelEvent example</h3>
<div style="font-size:12px; padding:5px; border:1px solid #ccc;"
onwheel="wheelHandler(event)">
Hello Everyone!
<div>
</body>
</html>
wheelevents-example.js
function wheelHandler(evt) {
var fontSize = evt.target.style.fontSize;// 12px, 13px,...
var value = Number(fontSize.substr(0, fontSize.length-2)); // 12, 13,..
// Scrolling up
if (evt.deltaY < 0) {
if(value < 50) {
value++;
}
}
// Scrolling down
if(evt.deltaY > 0) {
if(value > 5) {
value--;
}
}
evt.target.style.fontSize = value+"px";
}
