GlobalEventHandlers.onpointerdown - Web APIs 编辑

The GlobalEventHandlers event handler onpointerdown is used to specify the event handler for the pointerdown event, which is fired when the pointing device is initially pressed. This event can be sent to Window, Document, and Element objects.

This is functionally equivalent to the mousedown event when generated due to user activity with a mouse or mouse-compatible device. If the pointerdown event isn't canceled through a call to preventDefault(), most user agents will fire a mousedown event, so that sites not using pointer events will work.

You can also use addEventListener() to add a listener for pointerdown events.

Syntax

target.onpointerdown = downHandler;

var downHandler = target.onpointerdown;

Value

A Function to handle the pointerdown event for the target Element, Document, or Window. It receives as input the PointerEvent describing the pointerdown event.

Example

This example demonstrates how to watch for and act upon pointerdown events using onpointerdown. You could also use addEventListener(), of course.

JavaScript

First, let's look at the JavaScript code that handles the pointerdown event.

var targetBox = document.getElementById("target");

targetBox.onpointerdown = handleDown;

function handleDown(evt) {
  var action;

  switch(evt.pointerType) {
    case "mouse":
      action = "clicking";
      break;
    case "pen":
      action = "tapping";
      break;
    case "touch":
      action = "touching";
      break;
    default:
      action = "interacting with";
      break;
  }

  targetBox.textContent = `Thanks for ${action} me!`;
  evt.preventDefault();
}

This uses onpointerdown to establish the function handleDown() as the event handler for pointer down events.

The handleDown() function, in turn, looks at the value of pointerType to determine what kind of pointing device was used, then uses that information to customize a string to replace the contents of the target box.

Then the event's preventDefault() method is called to ensure that the mousedown event isn't triggered, potentially causing events to be handled twice if we had a handler for those events in case Pointer Event support is missing.

We also have a handler for pointerup events:

targetBox.onpointerup = handleUp;

function handleUp(evt) {
  targetBox.textContent = "Tap me, click me, or touch me!";
  evt.preventDefault();
}

This code's job is to just restore the original text into the target box after the user's interaction with the element ends (for example, when they release the mouse button, or when they lift the stylus or finger from the screen).

In addition, the event's preventDefault() method is called to ensure that the mouseup event isn't triggered unnecessarily.

<div id="target">
  Tap me, click me, or touch me!
</div>

#target {
  width: 400px;
  height: 30px;
  text-align: center;
  font: 16px "Open Sans", "Helvetica", sans-serif;
  color: white;
  background-color: blue;
  border: 2px solid darkblue;
  cursor: pointer;
  user-select: none;
  -moz-user-select: none;
  -webkit-user-select: none;
  -ms-user-select: none;
}

Result

The resulting output is shown below. Try tapping, clicking, or touching the box and see what happens. For full effect, try it with a variety of pointer types.

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Pointer events
• Using Pointer Events
• Coordinate systems
• Document: pointerdown event
• HTMLElement: pointerdown event