jQuery源码 02--(3043 , 3183) Deferred : 延迟对象 : 对异步的统一管理

Posted 2020-09-20 672530440

//延迟对象
jQuery.extend({

    Deferred: function( func ) {
        var tuples = [//resolve完成、reject未完成、notify进行中类似于fire，done、fail、progress回调函数的方法类似于add，jQuery.Callbacks()创建回调对象实现回调方法。映射数组。
                // 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 ],//得到状态
                                fn = jQuery.isFunction( fns[ i ] ) && fns[ i ];//是函数得到这个函数，不是函数返回假，
                            // 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();
                },
                //jQuery.extend( obj, promise )这个promise是根据函数闭包，向上去找的，把promise复制给obj，
                promise: function( obj ) {
                    return obj != null ? jQuery.extend( obj, promise ) : promise;
                }
            },
            deferred = {};

        // Keep pipe for back-compat
        promise.pipe = promise.then;

        // 映射数组进行映射的函数
        jQuery.each( tuples, function( i, tuple ) {
            var list = tuple[ 2 ],//jQuery.Callbacks("once memory")
                stateString = tuple[ 3 ];//resolved

            // promise[ done | fail | progress ] = list.add=jQuery.Callbacks("once memory").add方法
            promise[ tuple[1] ] = list.add;

            // Handle state
            if ( stateString ) {
                list.add(function() {
                    // state = [ resolved | rejected ]
                    state = stateString;

                // [ reject_list | resolve_list ].disable; progress_list.lock
                }, tuples[ i ^ 1 ][ 2 ].disable, tuples[ 2 ][ 2 ].lock );
            }

            // deferred[ resolve | reject | notify ]
            deferred[ tuple[0] ] = function() {//给deferred这个json赋值
                deferred[ tuple[0] + "With" ]( this === deferred ? promise : this, arguments );
                return this;
            };
            // deferred[ resolveWith | rejectWith | notifyWith ]=jQuery.Callbacks("once memory").fireWith方法
            deferred[ tuple[0] + "With" ] = list.fireWith;//继续给deferred这个json赋值
        });

        // 把promise复制给deferred，deferred比promise多了3个方法，
        promise.promise( deferred );

        // Call given func if any
        if ( func ) {
            func.call( deferred, deferred );
        }

        // All done!
        return deferred;
    },

    // Deferred helper
    when: function( subordinate /* , ..., subordinateN */ ) {
        var i = 0,
            resolveValues = core_slice.call( arguments ),
            length = resolveValues.length,

            // 未完成函数的计数器，jQuery.isFunction( subordinate.promise ):subordinate的返回值是不是函数。
            remaining = length !== 1 || ( subordinate && jQuery.isFunction( subordinate.promise ) ) ? length : 0,

            // the master Deferred. If resolveValues consist of only a single Deferred, just use that.
            deferred = remaining === 1 ? subordinate : jQuery.Deferred(),

            // Update function for both resolve and progress values
            updateFunc = function( i, contexts, values ) {
                return function( value ) {
                    contexts[ i ] = this;
                    values[ i ] = arguments.length > 1 ? core_slice.call( arguments ) : value;
                    if( values === progressValues ) {
                        deferred.notifyWith( contexts, values );
                    } else if ( !( --remaining ) ) {//减到0时触发resolveWith方法，
                        deferred.resolveWith( contexts, values );
                    }
                };
            },

            progressValues, progressContexts, resolveContexts;

        // add listeners to Deferred subordinates; treat others as resolved
        if ( length > 1 ) {
            progressValues = new Array( length );
            progressContexts = new Array( length );
            resolveContexts = new Array( length );
            for ( ; i < length; i++ ) {
                if ( resolveValues[ i ] && jQuery.isFunction( resolveValues[ i ].promise ) ) {
                    resolveValues[ i ].promise()//返回值
                        .done( updateFunc( i, resolveContexts, resolveValues ) )//触发完成函数
                        .fail( deferred.reject )//触发失败函数
                        .progress( updateFunc( i, progressContexts, progressValues ) );
                } else {
                    --remaining;
                }
            }
        }

        //计时器为0时执行resolveWith方法，
        if ( !remaining ) {
            deferred.resolveWith( resolveContexts, resolveValues );
        }

        return deferred.promise();//执行done方法，
    }
});