1.for循环

for(var i = 0;i<5;i++){
    console.log(i)
}

2.for in循环

let obj = {a:1, b:2, c:3};
for (let prop in obj) {  //prop指对象的属性名
console.log(prop, obj[prop]);
}   //输出: a,1 b,2 c,3

3.for of循环

let arr = ['123','qwewq','sfds'];
for(let item of arr){
console.log(item); //item指的的就是数组每一项的值。不是索引。
}
//输出 '123' 'qwewq' 'sfds'

4.forEach循环

let arr = ['123','qwewq','sfds'];
myArray.forEach(function (value, index) {
    console.log(value,index);
});
// 输出结果 '123',1  'qwewq',2  'sfds',3

5.map循环

    let arr = ['123','qwewq','sfds'];
    arr.map(function(value,index){
    console.log(value,index);
    });
    // 输出结果 '123',1  'qwewq',2  'sfds',3