JS循环for、for...of、for...in

循环数组

      let arr = [1, 2, 3, 4, 5, 6, 7, 8]
        //1
        //2
        //3
        //4
        //5
        //6
        //7
        //8
        // for
        for (var i = 0; i < arr.length; i++) {
   
            console.log('arr[i]===', arr[i], "===", i);
        }
        console.log('==========',);

        //map filter same every find forEach
        console.log('==========',);
        // for in 
        let arrObj = [{
   
            name: 'zjq',
            age: 18
        }, {
   
            name: 'zrh',
            age: 188
        }, {
   
            name: 'zzz',
            age: 1888
        }, {
   
            name: 'hhh',
            age: 18888
        }, {
   
            name: 'qqq',
            age: 188888
        },]

        for (let i = 0; i < 5; i++) {
   
            console.log('arrObj[i]===', arrObj[i]);
        }
        console.log('==========',);
        // for in 
        for (let key in arrObj) {
   
            console.log('obj[key]===', arrObj[key], "===key", key);
        }
        //   
        for (let key of arrObj) {
   
            console.log('arrObj===', arrObj, "===key", key);
        }

for: 数组[下标]
for…of：key 每一项
for…in key下标

循环对象

    let obj = {
    name: 'zjq', age: 18, habby: '123456', 0: 123 }

        console.log('==========',);
        for (let key in obj) {
   
            console.log('obj[key]===', obj[key], "===key", key);
        }

for…in：key键值 对象[key]键值的value