### 1.`foreach` ~~~ var arr = [5,2,3,4]; arr.forEach(function(value,index){ console.log(index); }) ~~~ Jquery--each ~~~ var arr = [5,2,3,4]; $.each(arr,function(index,value){ console.log(index); }) ~~~ clone数组 ~~~ const items = ['item1', 'item2', 'item3']; const copy = []; for (let i=0; i<items.length; i++) { copy.push(items[i]) } ~~~ ~~~ const items = ['item1', 'item2', 'item3']; const copy = []; items.forEach(function(item){ copy.push(item) }); ~~~ ### 2.of ~~~ var arr = [5,2,3,4]; for(let value of arr){ console.log(value); } ~~~ ### 3. for in ~~~ for(let k in arr){ console.log(arr[k]); } ~~~ ### 4.map ~~~ var arr = [5,2,3,4]; arr.map(function(value,index){ console.log(index); }) ~~~ ### 6. for循环 ~~~ for(let i=0;i<arr.length;i++){ console.log(arr[i]) ~~~