[js高手之路] 设计模式系列课程

迭代器是指通过一种形式依次遍历数组，对象，或者类数组结构中的每个元素. 常见的有jquery中的each方法, ES5自带的forEach方法. 下面我们就来自定义一个类似jquery或者ES5的迭代器方法

1         function each( arr, fn ) {
2             for( var i = 0, len = arr.length; i < len; i++ ){
3                 fn.call( arr, arr[i], i );
4             }
5         }
6         each( [ 'zhangsan', 'lisi', 'ghostwu' ], function( val, key ){
7             console.log( this, val, key );
8         });

输出结果：

["zhangsan", "lisi", "ghostwu"] "zhangsan" 0

["zhangsan", "lisi", "ghostwu"] "lisi" 1

["zhangsan", "lisi", "ghostwu"] "ghostwu" 2

二、利用迭代器，判断两个数组的长度和对应的位置的值是否相等

        function each( arr, fn ) {
            for( var i = 0, len = arr.length; i < len; i++ ){
                fn.call( arr, arr[i], i );
            }
        }
        function isEqual( arr1, arr2 ){
            var flag = false;
            if( arr1.length != arr2.length ){
                throw new Error( '数组的长度不相等' );
            }
            each( arr1, function( val, key ){
                if ( val != arr2[key] ) {
                    throw new Error('数组的第' + (key+1) + '项不相等');
                }
            });
            return true;
        }
        console.log( isEqual( [ 10, 20, 30 ], [ 10, 20, 30 ] ) );

三、另一种迭代器

        function Iterator( obj ){
            var curInd = 0;
            var next = function(){
                curInd += 1;
            };
            var isDone = function(){
                return curInd >= obj.length;
            };
            var current = function(){
                return obj[curInd];
            };
            return {
                next : next,
                isDone : isDone,
                current : current
            };
        }
        var obj = null;
        obj = Iterator( [ 10, 20, 30 ] );
        console.log( obj.current(), obj.isDone() ); // 10, false
        obj.next();
        console.log( obj.current(), obj.isDone() ); // 20, false
        obj.next();
        console.log( obj.current(), obj.isDone() ); // 30, false
        obj.next();
        console.log( obj.current(), obj.isDone() ); // undefined, true

四，使用上面的迭代器，改写两个数组的比较

        function Iterator( obj ){
            var curInd = 0;
            var next = function(){
                curInd += 1;
            };
            var isDone = function(){
                return curInd >= obj.length;
            };
            var current = function(){
                return obj[curInd];
            };
            return {
                next : next,
                isDone : isDone,
                current : current
            };
        }

        function compare( it1, it2 ){
            while( !it1.isDone() && !it2.isDone() ){
                if( it1.current() != it2.current() ){
                    throw new Error( '数组不相等' );
                }
                it1.next();
                it2.next();
            }
            return true;
        }

        var Iterator1 = Iterator([ 10, 20, 30 ]);
        var Iterator2 = Iterator([ 10, 20, 30 ]);

        console.log( compare( Iterator1, Iterator2 ) );