handbook|forin和forof

📢 数组中forin迭代到的属性类型为字符串类型

forof

let a = [4, 5, 6, 7];
for (let v of a)  {
    console.log(v, typeof v)
}
// 4 number
// 5 number
// 6 number
// 7 number

forin

let a = [4, 5, 6, 7];
for (let idx in a)  {
    console.log(idx, typeof idx)
}
// 0 string
// 1 string
// 2 string
// 3 string
typeof 'e' // 'string'

Set元素可用for-of遍历得到

Set + for of

let a = new Set();
a.add(1);
a.add(2);
for(let key of a) console.log(key, typeof key)
// 1 number
// 2 number
for(let key in a) console.log(key, typeof key)
// none