jquery源码分析(四)——回调对象 Callbacks

var rnotwhite = (/\S+/g);//匹配空格，返回数组

// String to Object options format cache
var optionsCache = {};

// Convert String-formatted options into Object-formatted ones and store in cache
function createOptions( options ) {
    var object = optionsCache[ options ] = {};
    jQuery.each( options.match( rnotwhite ) || [], function( _, flag ) {//接受的字符串的组合传参数，可以使用空格分割
        object[ flag ] = true;
    });
    return object;
}

/*
 * Create a callback list using the following parameters:

 * By default a callback list will act like an event callback list and can be
 * "fired" multiple times.
 *
 * Possible options://这里提供四个可选参数once、memory、unique、stopOnFalse 对函数队列进行特殊控制。
 */
jQuery.Callbacks = function( options ) {

    // Convert options from String-formatted to Object-formatted if needed
    // (we check in cache first)
    options = typeof options === "string" ?
        ( optionsCache[ options ] || createOptions( options ) ) :
        jQuery.extend( {}, options );

    var // Flag to know if list is currently firing
        firing,
        // Last fire value (for non-forgettable lists)
        memory,
        // Flag to know if list was already fired
        fired,
        // End of the loop when firing
        firingLength,
        // Index of currently firing callback (modified by remove if needed)
        firingIndex,
        // First callback to fire (used internally by add and fireWith)
        firingStart,
        // Actual callback list
        list = [],
        // Stack of fire calls for repeatable lists
        stack = !options.once && [],//传递once参数后，则回调执行完毕之后，list会被清空([])或置为undefined
        // Fire callbacks
        fire = function( data ) {//闭包方法
            memory = options.memory && data;
            fired = true;//用来判断回调队列是否被执行过一次
            firingIndex = firingStart || 0;//上次fire的位置，用作设置memory时，add之后直接触发回调。
            firingStart = 0;
            firingLength = list.length;
            firing = true;
            for ( ; list && firingIndex < firingLength; firingIndex++ ) {
                if ( list[ firingIndex ].apply( data[ 0 ], data[ 1 ] ) === false && options.stopOnFalse ) {//判断是否需要判读回调返回值
                    memory = false; // To prevent further calls using add---//强制修改memory
                    break;
                }
            }
            firing = false;
            if ( list ) {
                if ( stack ) {//是否为false，初始化时是通过是否传递once来控制，
                    if ( stack.length ) {
                        fire( stack.shift() );
                    }
                } else if ( memory ) {//这里清空目的在于，add之后直接fire新添加的回调。
                    list = [];
                } else {
                    self.disable();
                }
            }
        },
        // Actual Callbacks object
        self = {
            // Add a callback or a collection of callbacks to the list
            add: function() {
                if ( list ) {
                    // First, we save the current length
                    var start = list.length;
                    (function add( args ) {//添加回调list集合
                        jQuery.each( args, function( _, arg ) {
                            var type = jQuery.type( arg );
                            if ( type === "function" ) {
                                if ( !options.unique || !self.has( arg ) ) {
                                    list.push( arg );
                                }
                            } else if ( arg && arg.length && type !== "string" ) {
                                // Inspect recursively
                                add( arg );
                            }
                        });
                    })( arguments );
                    // Do we need to add the callbacks to the
                    // current firing batch?
                    if ( firing ) {
                        firingLength = list.length;
                    // With memory, if we‘re not firing then
                    // we should call right away
                    } else if ( memory ) {//这里如果option.memory有值的话，memory已经被修改为[context,arguments]
                        firingStart = start;
                        fire( memory );
                    }
                }
                return this;
            },
            // Remove a callback from the list
            remove: function() {//从回调队列中 删除函数。
                if ( list ) {
                    jQuery.each( arguments, function( _, arg ) {
                        var index;
                        while ( ( index = jQuery.inArray( arg, list, index ) ) > -1 ) {
                            list.splice( index, 1 );
                            // Handle firing indexes
                            if ( firing ) {
                                if ( index <= firingLength ) {
                                    firingLength--;
                                }
                                if ( index <= firingIndex ) {
                                    firingIndex--;
                                }
                            }
                        }
                    });
                }
                return this;
            },
            // Check if a given callback is in the list.
            // If no argument is given, return whether or not list has callbacks attached.
            has: function( fn ) {
                return fn ? jQuery.inArray( fn, list ) > -1 : !!( list && list.length );
            },
            // Remove all callbacks from the list
            empty: function() {//清空回调队列
                list = [];
                firingLength = 0;
                return this;
            },
            // Have the list do nothing anymore
            disable: function() {//整个回调队列失效
                list = stack = memory = undefined;
                return this;
            },
            // Is it disabled?
            disabled: function() {
                return !list;
            },
            // Lock the list in its current state
            lock: function() {//在当前状态下锁死
                stack = undefined;
                if ( !memory ) {
                    self.disable();
                }
                return this;
            },
            // Is it locked?
            locked: function() {
                return !stack;
            },
            // Call all callbacks with the given context and arguments
            fireWith: function( context, args ) {
                if ( list && ( !fired || stack ) ) {
                    args = args || [];
                    args = [ context, args.slice ? args.slice() : args ];
                    if ( firing ) {
                        stack.push( args );
                    } else {
                        fire( args );//若$.Callback调用时设置memory，则会闭包中memory被修改为此时的args<==>[context,args]
                    }
                }
                return this;
            },
            // Call all the callbacks with the given arguments
            fire: function() {//切换执行上下问
                self.fireWith( this, arguments );
                return this;
            },
            // To know if the callbacks have already been called at least once
            fired: function() {//判断回调队列已经被触发过一次
                return !!fired;
            }
        };

    return self;
};