js中forEach,for in,for of的区别

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<script>

    var arr = [1,2,3];

    arr.four = 4;

    console.log(arr);

    arr.forEach(value => {

        /*if(value > 2) {

            break

    }*/

        console.log(value)//1,2,3

    })

    for(let i in arr) {

        console.log(i); // '0' '1' '2' 'four' 相当于对象的key值

        console.log(arr[i]) // 1,2,3,4 相当于对象的value值

    }

    for (let i of arr) {

        if(i > 2) {

            break

        }

        console.log(i); // 1,2,3  数值中的每一项的值

        console.log(arr[i]);//2,3,undefined 相当于arr[1],arr[2],arr[3]

    }

    for (let i of 'my') {

        console.log(i); // 'm' 'y'

    }

    for (let i of arr) {

        if(i > 2) {

            break

        }

        console.log(i); // 1,2

    }

</script>

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总结：如果遍历数组最好用for of,遍历对象用for in
for of遍历数组和forEach遍历数组的区别：for of能用break语句，forEach不能

巴特西

js中forEach,for in,for of的区别

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