Js Bubbling Event Blocking

1. Event Objectives

The event object is now stored in the event handler for the variable event. The Event.target property holds the target element where the event occurred. This attribute is specified in the DOM API, but is not implemented by all browsers. jquery makes the necessary extensions to this event object so that this property can be used in any browser. With. Target, you can determine the element in the DOM that first received the event (that is, the element that was actually clicked). Furthermore, we know that this refers to the DOM element that handles the event, so you can write the following code:
$ (document). Ready (function () {
$ (' #switcher '). Click (Function (event) {
$ (' #switcher. Button '). Toggleclass (' hidden ');
})
})

$ (document). Ready (function () {
$ (' #switcher '). Click (Function (event) {
if (event.target==this) {
$ (' #switcher. Button '). Toggleclass (' hidden ');
}
})
})
The code at this point ensures that the clicked element is <div id= "switcher" >, not another descendant element. Clicking the button now does not collapse the style converter, and clicking the border will trigger the collapse operation. However, clicking a label also doesn't happen because it is also a descendant element. In fact, we can not put the check code here, but by modifying the behavior of the button to achieve the goal.

2. Stop Event Propagation

The event object also provides a. Stoppropagation () method that can completely block event bubbling. Similar to. Target, this method is a pure JavaScript feature, but it is not safe to use in a cross-browser environment. However, we can safely use this method as long as we register all event handlers with jquery.

Below, we will delete the check statement that we just added event.target = = This and add some code to the button's click handler:

$ (document). Ready (function () {
$ (' #switcher. Button '). Click (Funtion (Event) {
......
Event.stoppropagation ();
})
})

As before, you need to add a parameter to the function that is used as the click handler to access the event object. Then, by simply calling Event.stoppropagation (), you can avoid all other DOM elements in response to this event. As a result, clicking on the button's event is handled by the button and will only be handled by the button. Click elsewhere in the style converter to collapse and expand the entire area.

3. Default Action

If we register the click event handler with an anchor element instead of an outer layer of <div>, we face another problem: when the user clicks the link, the browser loads a new page. This behavior is not the same concept as the event handler we are discussing, it is the default action for clicking the anchor element. Similarly, when the user presses the ENTER key after editing the form, it will touch the submit event of the publication, after which the form submission does not actually occur.

If we do not want to perform this default action, calling the. Stoppropagation () method on the event object does not help, because the default action does not occur in the normal event propagation stream. In this case, the. Preventdefault () method can terminate the event before triggering the default action.

Tip When certain validations are completed in the context of an event, the. Preventdefault () is usually used. For example, during form submission, we check whether the user has filled in the required fields, and if the user does not fill in the fields, then the default action needs to be blocked. We will discuss form validation in detail in the 8th chapter.

Event propagation and default operations are two sets of mechanisms that are independent of each other, and can terminate the other when either party occurs. If you want to stop event propagation and the default operation at the same time, you can return false in the event handler, which is a shorthand for calling. Stoppropagation () and. Preventdefault () at the same time on the event object.

Js Bubbling Event Blocking