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

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         function isEqual( arr1, arr2 ){ 7             var flag = false; 8             if( arr1.length != arr2.length ){ 9                 throw new Error( '数组的长度不相等' );10             }11             each( arr1, function( val, key ){12                 if ( val != arr2[key] ) {13                     throw new Error('数组的第' + (key+1) + '项不相等');14                 }15             });16             return true;17         }18         console.log( isEqual( [ 10, 20, 30 ], [ 10, 20, 30 ] ) );

三、另一种迭代器

1         function Iterator( obj ){ 2             var curInd = 0; 3             var next = function(){ 4                 curInd += 1; 5             }; 6             var isDone = function(){ 7                 return curInd >= obj.length; 8             }; 9             var current = function(){10                 return obj[curInd];11             };12             return {13                 next : next,14                 isDone : isDone,15                 current : current16             };17         }18         var obj = null;19         obj = Iterator( [ 10, 20, 30 ] );20         console.log( obj.current(), obj.isDone() ); // 10, false21         obj.next();22         console.log( obj.current(), obj.isDone() ); // 20, false23         obj.next();24         console.log( obj.current(), obj.isDone() ); // 30, false25         obj.next();26         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

1         function Iterator( obj ){ 2             var curInd = 0; 3             var next = function(){ 4                 curInd += 1; 5             }; 6             var isDone = function(){ 7                 return curInd >= obj.length; 8             }; 9             var current = function(){10                 return obj[curInd];11             };12             return {13                 next : next,14                 isDone : isDone,15                 current : current16             };17         }18 19         function compare( it1, it2 ){20             while( !it1.isDone() && !it2.isDone() ){21                 if( it1.current() != it2.current() ){22                     throw new Error( '数组不相等' );23                 }24                 it1.next();25                 it2.next();26             }27             return true;28         }29 30         var Iterator1 = Iterator([ 10, 20, 30 ]);31         var Iterator2 = Iterator([ 10, 20, 30 ]);32 33         console.log( compare( Iterator1, Iterator2 ) );