ES6, deep copy, shallow copy

One 、 Concept

ES6:ESMAScript6, new javascript Grammar standards ,2015 Officially launched in , in order to js Faster and more convenient

Two 、 Variable declarations

 var： Global scope
            Function scope
             No, if,switch,for,while,do,else Scope
            Variable promotion

 let：1. Local scope ( In pairs {} Enable )
        2. You can't raise variables
        3. Cannot declare repeatedly in a scope

const：1. let equally
            2. Variable names are recommended to be capitalized
            3. Declaration must be assigned
            4. Value type cannot be modified

3、 ... and 、 deconstruction

Put the array , object , Deconstruct into separate variables

• Array

var [a,b,,c=20,...rest]=[1,2,3,4,5,6];

• object

var {name,age,leg=20,...rest} = obj;

Four 、let

• var  You can declare variables
• let    You can also declare local scope variables （ In pairs {} Enable ）

1. let    local variable
2. Cannot repeat declaration
3. let You can't raise variables

var lis = document.querySelectorAll("ul li");
for(let i=0;i<lis.length;i++){
	lis[i].onclick = function(){alert(i)}
}

var h1 = document.querySelector("h1");
for(let i=9;i>=1;i--){
	// Delay 10-i Seconds to perform 
	setTimeout(function(){
		// Set the text value to i
		h1.innerText = i;
	},(10-i)*1000);
}

5、 ... and 、const

characteristic :

• const  It's a local variable
• Declaration must be assigned
• Cannot repeat declaration
• It is suggested to capitalize
• No variable promotion
• Value type cannot be modified

When to use const

1. When declared variables are not allowed to be modified , When it's a constant
2. When this pair probability will not be changed ( choice DOM node )

{
const PI = 3.1415926;
const PI;
console.log(PI);
}

{
const LIST = ["I","Hate","You"];
LIST.push("LOve");
console.log(LIST);
}

6、 ... and 、 Deep copy

Deep copy , Value type , And reference types are copied ( Don't affect each other )

Shallow copy , Value type copy , The reference type is reference

function deepCopy(obj){
	// If typeof  The value is object And not null
	if(typeof obj === 'object'&&obj!=null){
		var result;
		// If it's an array 
		if(obj instanceof Array){
			result = [];
			// Traversal array , Execute Copy 
			for(var i=0;i<obj.length;i++){
				// The value of the current subscript is the result of executing a deep copy 
				result[i]=deepCopy(obj[i])
			}
		}else{
			// If it's an object 
			result = {};
			for(var k in obj){
				// Perform traversal of deep copy objects 
				result[k] = deepCopy(obj[k])
			}
		}
		// The result returned 
		return result;
	}else{
		// Value type alive null Alive   Function directly returns 
		return obj;
	}
}

7、 ... and 、 Shallow copy

Deep copy , Values and reference types are copied

var obj = {name:"mumu",age:18,friend:["A","B","C"]}
var obj1 = {};
for(var k in obj){
    obj1[k] = obj[k];
}