javascript - $.Deferred().promise 与 $.get().promise

Question

我正在尝试以下代码:

var x=$.get();
x.promise();

var y=new $.Deferred();
y.promise();

用于比较$.Deferred().promise 和 $.get().promise。 在这两种情况( x.promise() 和 y.promise() )中，Chrome 调试器都会将我引导至 jQuery 源代码的同一行:

promise: function( obj ) {
    return obj != null ? jQuery.extend( obj, promise ) : promise;
}  

但是，x.promise==y.promise 返回false!!! 为什么？我无法给出解释...

我需要一些帮助。谢谢

Answer 1

伊利亚斯 这是因为对象 defer 和对象 promise 不是同一个实例，即使它们是从相同的代码创建的...... 每次调用 jQuery.Deferred 方法都会创建新对象。

Deferred: function( func ) {
    // notice, these define is in the Deferred method, every time is whole new object
    var tuples = [
            // action, add listener, listener list, final state
            [ "resolve", "done", jQuery.Callbacks("once memory"), "resolved" ],
            [ "reject", "fail", jQuery.Callbacks("once memory"), "rejected" ],
            [ "notify", "progress", jQuery.Callbacks("memory") ]
        ],
        state = "pending",
        promise = {
            state: function() {
                return state;
            },
            always: function() {
                deferred.done( arguments ).fail( arguments );
                return this;
            },
            then: function( /* fnDone, fnFail, fnProgress */ ) {
                var fns = arguments;
                return jQuery.Deferred(function( newDefer ) {
                    jQuery.each( tuples, function( i, tuple ) {
                        var action = tuple[ 0 ],
                            fn = jQuery.isFunction( fns[ i ] ) && fns[ i ];
                        // deferred[ done | fail | progress ] for forwarding actions to newDefer
                        deferred[ tuple[1] ](function() {
                            var returned = fn && fn.apply( this, arguments );
                            if ( returned && jQuery.isFunction( returned.promise ) ) {
                                returned.promise()
                                    .done( newDefer.resolve )
                                    .fail( newDefer.reject )
                                    .progress( newDefer.notify );
                            } else {
                                newDefer[ action + "With" ]( this === promise ? newDefer.promise() : this, fn ? [ returned ] : arguments );
                            }
                        });
                    });
                    fns = null;
                }).promise();
            },
            // Get a promise for this deferred
            // If obj is provided, the promise aspect is added to the object
            promise: function( obj ) {
                return obj != null ? jQuery.extend( obj, promise ) : promise;
            }
        },
        deferred = {};