处世应当谦虚,切忌轻人傲世。——佚名

简单说下区别:

for...in遍历出来的是key

1
2
3
4
5
6
7
8
9
10
var obj = {a:1, b:2, c:3};

for (var prop in obj) {
console.log("obj." + prop + " = " + obj[prop]);
}

// Output:
// "obj.a = 1"
// "obj.b = 2"
// "obj.c = 3"

for...of遍历出来的是元素

1
2
3
4
5
6
7
8
9
const array1 = ['a', 'b', 'c'];

for (const element of array1) {
console.log(element);
}

// Expected output: "a"
// Expected output: "b"
// Expected output: "c"

for await...offor...of差不多,但支持遍历由Promise组成的可迭代对象(如数组),使用时会自动await直到Promise执行结束才执行

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
var asyncIterable = {
[Symbol.asyncIterator]() {
return {
i: 0,
next() {
if (this.i < 3) {
return Promise.resolve({ value: this.i++, done: false });
}

return Promise.resolve({ done: true });
}
};
}
};

(async function() {
for await (num of asyncIterable) {
console.log(num);
}
})();

// 0
// 1
// 2