$(document) . on (‘ click’,’# id’，function(){}) vs $(’# id’) . on (‘ click’，function(){})

我想知道

$(document).on('click', '#id', function(){});

还有

$('#id').on('click', function(){});

我还没有找到任何关于这两者之间是否有区别的信息，如果有的话，区别可能是什么。

有没有人能解释一下到底有没有区别？

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最佳答案

The first example demonstrates event delegation. The event handler is bound to an element higher up the DOM tree (in this case, the document) and will be executed when an event reaches that element having originated on an element matching the selector.

This is possible because most DOM events bubble up the tree from the point of origin. If you click on the #id element, a click event is generated that will bubble up through all of the ancestor elements (side note: there is actually a phase before this, called the 'capture phase', when the event comes down the tree to the target). You can capture the event on any of those ancestors.

The second example binds the event handler directly to the element. The event will still bubble (unless you prevent that in the handler) but since the handler is bound to the target, you won't see the effects of this process.

By delegating an event handler, you can ensure it is executed for elements that did not exist in the DOM at the time of binding. If your #id element was created after your second example, your handler would never execute. By binding to an element that you know is definitely in the DOM at the time of execution, you ensure that your handler will actually be attached to something and can be executed as appropriate later on.

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Consider following code

<ul id="myTask">
<li>Coding</li>
<li>Answering</li>
<li>Getting Paid</li>
</ul>

Now, here goes the difference

// Remove the myTask item when clicked.
$('#myTask').children().click(function () {
$(this).remove()
});

Now, what if we add a myTask again?

$('#myTask').append('<li>Answer this question on SO</li>');

Clicking this myTask item will not remove it from the list, since it doesn't have any event handlers bound. If instead we'd used .on, the new item would work without any extra effort on our part. Here's how the .on version would look:

$('#myTask').on('click', 'li', function (event) {
$(event.target).remove()
});

Summary:

The difference between .on() and .click() would be that .click() may not work when the DOM elements associated with the .click() event are added dynamically at a later point while .on() can be used in situations where the DOM elements associated with the .on() call may be generated dynamically at a later point.


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