Returning True and False in OnTouch
The `onTouch` event handler in JavaScript is commonly used to respond to touch interactions on elements. While it doesn’t inherently return true or false, understanding how its execution flow impacts subsequent actions is crucial.
Understanding OnTouch Execution
- **Event Propagation:** When a touch event occurs, the browser initiates an event propagation process. This involves the event bubbling up through the DOM tree, starting from the targeted element and going towards its ancestors.
- **Event Handling:** As the event bubbles up, any `onTouch` handlers associated with the elements encountered are executed. If a handler returns `false`, it prevents further propagation of the event to ancestor elements.
Default Browser Actions
Many touch events have default browser actions associated with them. These actions might include:
- **Scrolling:** On a long page or scrollable area, touch interactions typically initiate scrolling.
- **Zooming:** Pinch gestures on touchscreens often trigger zooming.
- **Text Selection:** Long-press on text might trigger text selection.
Controlling Default Behavior
You can control whether default browser actions occur after a touch event by manipulating the return value of your `onTouch` handler:
| Return Value | Effect |
|---|---|
| `true` | Allows default browser actions to proceed. |
| `false` | Cancels default browser actions. |
Example: Preventing Scrolling
<div id="myDiv" style="height: 500px; overflow: auto;" onTouchStart="return false;"><p>This content can't be scrolled.</p></div>
In this example, the `onTouchStart` handler returns `false`, preventing the `myDiv` element from scrolling even though its `overflow` property is set to `auto`.
Important Notes
- **Specific Event Types:** The effect of returning `true` or `false` might differ depending on the specific touch event (e.g., `onTouchStart`, `onTouchMove`, `onTouchEnd`). Consult browser documentation for detailed behavior.
- **Event Listeners:** Modern JavaScript often utilizes event listeners instead of inline event handlers. In this case, you can use `event.preventDefault()` to prevent default actions within the listener function.