Jquery promise wait to ajax end

问题:

I'm getting predefined values, which i have to insert into two selects:

<div id="wrapper">
    <select id="first">
        <option value="1">1</option>
        <option value="2">2</option>
        <option value="3">3</option>
    </select>
    <select id="second"></select>
</div>

Options inside #second depends on selected value in #first. This options are loaded via ajax:

$('#first').change( function() {
        $.ajax({
            url: "giveMeValues.phpOrWhatever"
        }).done(function() {
            // just simulating data from ajax call
            $('#second').append(
                '<option value="a">a</option>'+
                '<option value="b">b</option>'+
                '<option value="c">c</option>'
            );
        });
    });

The problem is, I can set value of #second after ajax data will be loaded. So following code will of course not work:

$('#first').val('2').change();
$('#second').val('b').change();

So i tried to use .promise() to wait untill ajax call inside change handler will be completed:

$('#first').val('2').change();
    $('#wrapper').promise().then( function() {
        $('#second').val('b');
        console.log('setting value...');
    });

But it doesn't work. My question is: how i can wait to end of ajax call, and then set #second value?

Here you have fiddle for this problem: http://jsfiddle.net/W2nVd/

Thanks for your time.

回答1:

You need to set the promise from the ajax like so:

(function($) {
    // Our Ajax promise variable
    var promise;

    $('#first').change( function() {
        // Set the ajax promise variable
        promise = $.ajax({
            url: "#"
        }).done(function() {
            $('#second').append(
                '<option value="a">a</option>'+
                '<option value="b">b</option>'+
                '<option value="c">c</option>'
            );
            console.log('appending new content...');
        });
    });

    $('#first').val('2').change();
    // the var `promise` was set on the line above when it executed 
    // the `change()` callback
    promise.promise().done( function() {
        $('#second').val('b');
        console.log('setting value...');
    });

})(jQuery);

JSFiddle: http://jsfiddle.net/W2nVd/2/

回答2:

Perhaps I'm missing some of your workflow requirements, but can't you just set the value of #second after you append the options?

$.ajax({
            url: "#"
        }).done(function() {
            $('#second').empty().append(
                '<option value="a">a</option>'+
                '<option value="b">b</option>'+
                '<option value="c">c</option>'
            );
            $('#second').val('b');
            console.log('appending new content...');
        });

Updated fiddle: http://jsfiddle.net/W2nVd/1/

回答3:

.done() is exactly what you are searching for just put it inside..like so

try ...

$('#first').change( function() {
    $.ajax({
        url: "giveMeValues.phpOrWhatever"
    }).done(function() {
        // just simulating data from ajax call
        $('#second').append(
            '<option value="a">a</option>'+
            '<option value="b" selected="selected">b</option>'+
            '<option value="c">c</option>'
        );
    });
});

.... or.....

$('#first').change( function() {
    $.ajax({
        url: "giveMeValues.phpOrWhatever"
    }).done(function() {
        // just simulating data from ajax call
        $('#second').append(
            '<option value="a">a</option>'+
            '<option value="b">b</option>'+
            '<option value="c">c</option>'
        );
        $('#second').val('b'); // change value after options are available


    });
});