jQuery .on() method doesn't see new elements

问题:

I'm getting a JSON element and building a list from its items like this:

getTitles: function(data) {
    data = data || {};
    var list = [];

    $.getJSON(
        '/titles',
        data,
        function(data) {
            $.each(data.data, function(key, val) {
                list.push(
                    '<li><a href="'+ val.href +'">'+ val.title +'</a><span class="count">'+ val.count +'</span></li>'
                )
            });

            $('#title-items').html(list.join(''));
        }
    );
}

And I'm binding click event for a elements like this:

$('a').on('click', function(e) {
    alert('clicked');
    e.preventDefault();
});

Old a elements shows alert but new ones follow URL. Event handler doesn't work for new ones. How can I solve this?

回答1:

You are not using the correct code to get live functionality.

$('#title-items').on('click', 'a', function(e) {
    alert('clicked');
    e.preventDefault();
});

1. First, select your common ancestor element (#title-items in this example). You can use document here too if you want to handle all a elements.
2. Pass the event type (on), then the sub selector (a), and then the callback function for the event.

Now, when click events bubble up to #title-items, it will check to see if the element is an a element, and if so, fire the callback.

回答2:

You want to use event delegation to capture events triggered on events that are present in the DOM at any point in time:

$(<root element>).on('click', 'a', function(e) {
    alert('clicked');
    e.preventDefault();
});

UPDATE - In this example the <root element> is an ancestor of the links to which you are binding that is present in the DOM at the time of binding.

The basic idea is that since we can't attach an event handler to a DOM element not yet in the DOM, we attach the event handler to an ancestor element and wait for the event to bubble up to the ancestor element. Once the event reaches the ancestor event the event.target property is checked to see what was the originally clicked element.

回答3:

You can use the arrive.js library (it uses MutationObserver internally).

document.arrive('a', function(){
    // 'this' refers to the newly created element
    var newElem = this;
});