for in, for of detailed explanation

for in

Can be used in enumerable data => objects

enumerable data

property descriptor => enumerable

example

1. It can be used to traverse objects => attribute name,
such as:

there is an enumerable attribute above, which is to control whether the attribute can be enumerated

Also enumerates the enumerable property names on the object prototype

let obj = {
    
    
    name: "lihegui",
    gender: "nan",
    age: "22"
}
for (let item in obj) {
    
    
    console.log(item);
}
//	name
//	gender
//	age

2. It can be used to traverse the array => array subscript

let arr = ["lihegui", "fxp", "shuzu"]
for (let item in arr) {
    
    
    console.log(item);
}
//	0
//	1
//	2

3. Traverse the string => the subscript of the position of the character

let str = "lihegui"
for (let item in str) {
    
    
    console.log(item);
}
//	0
//	1
//	2
//	3
//	4
//	5
//	6

for of

Can be used in iterable data => array, string, Map, Set

for in traversal map set will be undefined

iterable data

As long as a data implements the Iterator interface, the data will have a property called [Symbol.iterator].
For example, an array has a Synbol.iterator property.

example

1. Traverse the array => each item of the array

let arr = ["lihegui", ["and", "lihegui"], "fxp", "shuzu"]
for (let item of arr) {
    
    
    console.log(item);
}
//	lihegui
//	['and','lihegui']
//	fxp
//	shuzu

2. Traverse the string => each character

let str = "lihegui"
for (let item of str) {
    
    
    console.log(item);
}
//	l
//	i
//	h
//	e
//	g
//	u
//	i

3. Traverse map => each item

let map = new Map([
    [1, 'one'],
    [2, 'two'],
    [3, 'three']
])
for (let item of map) {
    
    
    console.log(item);
}
//	[ 1, 'one' ]
//	[ 2, 'two' ]
//	[ 3, 'three' ]

4. Traverse set => each item

let set = new Set(["lihegui", "fxp"])
for (let item of set) {
    
    
    console.log(item);
}
//	lihegui
//	fxp