1. for ... in 语句

for (let variable in object)  { ... }

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Statements/for...in

以任意次序迭代一个对象的可枚举属性。

 

var obj = {a: 1, b: 2};
for (let i in obj) {
    console("key:" + i + ", value:" + obj[i]);
}

 

数组Array的遍历，i则为数字

 

2. 迭代器遍历

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Iterator

如Array

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach

 

arr.forEach((value, index) => {
     console.log(value);
});

 

 

3. for ... of 语句

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Statements/for...of

for...of语句在可迭代对象(包括 Array, Map, Set, String, TypedArray，arguments 对象等等)上创建一个迭代循环，对每个不同属性的属性值,调用一个自定义的有执行语句的迭代挂钩.

但对于普通对象是不适应的。原因是没有实现参考下文。

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Guide/iterable