[js高手之路] 设计模式系列课程 - 迭代器(1)

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 ) );