jquery's tips on event bubbling and event delegation and three implementation methods of preventing and allowing event bubbling

jquery's tips on event bubbling and event delegation and three implementation methods of preventing and allowing event bubbling_jquery

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Release： 2016-05-16 15:29:20

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First of all, everyone knows that there are two mechanisms when jQuery events are triggered, one is event delegation, and the other is event bubbling (the IE situation is not considered for the time being). Take the click event as an example, first attach a piece of code:

html:

<body>
<div id="box">
<p id="btn">我是按钮</p>
</div>
</body>
style:
.hid{
　display:none;
}

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script:

$('#box').click(function(){
 $(‘#btn').toggleClass(‘hid');
})
$('#btn').click(function(){
 alert('btn');
})

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The original intention of this code is that when I click #btn, I want to alert the "btn" string, and when I click #box, I want to hide #btn. However, in the actual execution When I click btn, it will first execute the btn event, and then execute the box event, that is, alert first, and then hide it. It is different from what we thought, so how to solve this problem? Here we need to think of the event bubbling mechanism, because when I click btn, the event will bubble up to the parent element until the document object.

JQuery versions after 1.7 (if I remember correctly) provide the .on() event to handle events of bound elements. Here we can use the .on() event and the stopPropagation() method to prevent events. Bubbling:

$('#box').on('click','#btn',function(e){
 e.stopPropagation()；
 alert(‘btn');
})
$('#box').click(function(){
 $(‘#btn').toggleClass(‘hid');
})

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Here I first used on to bind the #btn event, so that when the btn button is clicked, alert('btn'), but because my e.stopPropagation() prevents the event from bubbling, therefore, it does not The toggleClas event will be triggered; and when I click #box, the normal toggleClass event will be triggered;

I thought about it here, how to solve it if .on() is not used, similar to the native js, using addEventListener to monitor the clicked target, the code is not complicated:

$('#box‘).click(function(e) {
 if (e.target == this) {
  $(‘#btn').toggleClass(‘hid');
 }
})
$(‘#btn').click(function() {
 alert(‘btn');
})

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In this way, you can prevent events from bubbling up.

Of course, event bubbling is not all side effects. It is another type we are going to talk about, which is event delegation. Event delegation is based on event bubbling. For example, in the above example, you can assume# There are many elements between btn and #box. When I want to click on the innermost #btn, and want to trigger its corresponding event, then I can click on its peripheral elements and then determine whether the click is the target. The element is btn. If it is, then the event that triggers btn is actually the above example of .on(), which can be rewritten as:

$('body').on('click','#btn',function(e){
 alert(‘btn');
})

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Delegate the btn event to the click body for processing.

Finally, let’s analyze it carefully. In fact, event delegation and event bubbling are nothing more than two opposite directions of execution from a logical perspective. Event delegation is actually the process of event capture, which can be seen as a process of capturing from outside to inside; while event bubbling is a process of bubbling from inside to outside.

Blocking and allowing bubbling events of jquery (three implementation methods)

Bubbling or default events are not needed at certain times. Here we need some methods to prevent bubbling and default events. This article introduces three methods to prevent them to varying degrees. Interested Friends can learn about it, it may help you understand bubbling events

Sometimes we don’t want bubbling or default events to occur, so we need some jquery methods to prevent bubbling and default events.
Different levels of blocking can be achieved through the following three methods.

A: return false --->In event handler, prevents default behavior and event bubbling.

return false In event processing, you can prevent default events and bubbling events.

B: event.preventDefault()---> In event handler, prevent default event (allows bubbling).

event.preventDefault() can prevent default events but allow bubbling events to occur during event processing.

C: event.stopPropagation()---> In event handler, prevent bubbling (allows default behavior).

event.stopPropagation() can prevent bubbling but allow the default event to occur during event processing.