JavaScript shallow copy deep copy detailed

One, shallow copy

The most common manifestation of a shallow copy in reality is above the assignment , for example

<! DOCTYPE html>
From the example above, we modified the value of the Test2 array, and finally printed the test array, and found that the test also changed.
In fact, this is one of the lightest shallow copies, which is equivalent to test2=test this stage is to assign the storage address index in the test array to the TEST2 array, so two arrays are pointing to the same storage address .
In addition to this approach, a shallow copy can be achieved, as well as a shallow copy using slice and concat
For example: We test slice this method ( you can return the selected element as a new array from an existing array )
<script type= "Text/javascript" >    var arr=["Demo1", "Demo2", "Demo3"];    var arr2=arr.slice (0);    arr2[1]= "Test";    Console.log (arr);//["Demo1", "Demo2", "Demo3"]    console.log (ARR2);//["Demo1", "Test", "Demo3"]</script>
As we can see from the above example, a deep copy of the array is made using the slice method,
Similarly, the usage of concat is as follows ( used to concatenate two or more arrays into a new array)
<script type= "Text/javascript" >    var arr=["Demo1", "Demo2", "Demo3"];    var arr2=arr.concat ();    arr2[1]= "Test";    Console.log (arr);//["Demo1", "Demo2", "Demo3"]    console.log (ARR2);//["Demo1", "Test", "Demo3"]</script>
Why is this already a deep copy of what I call a shallow copy?
For both methods slice and concat are shallow copies, only the first layer in the array can be copied
Second, deep copy
1. Via the built-in JS function
function Deepcopy (o) {    return Json.parse (Json.stringify (o));} var a = {A:1,b:2,c:3};var b = deepcopy (a); B.A = 4;alert (A.A); 1        alert (B.A);//4, assigns a value of B.A to 4, does not affect the A object, A.A is still 1
This is a good way to understand that, for a single Object object,
First use the built-in json.stringify () function to convert it to the string "{" A ": 1," B ": 2}"
The resulting string is no longer associated with the original object, and the resulting string is converted to a new object through the Json.parse () function . {a:1, b:2}
The operation on the new object is completely independent from the old object and does not affect each other. The advantage of this method is easy to understand, using JS built-in functions to achieve, do not need too much overhead.
2. In its own way, it iterates through an array or object, returning a new array or object.
varSimplecopy =function (o) {if(o instanceof Array) {varn = [];  for(vari =0; i < o.length; ++i) {N[i]=O[i]; }        returnN; } Else if(o instanceof Object) {varn = {}         for(varIincho) {n[i]=O[i]; }        returnN; }}
3. How do I implement a copy containing an object or an array? Then it is done by a recursive copy.
varDeepcopy =function (o) {if(o instanceof Array) {varn = [];  for(vari =0; i < o.length; ++i) {N[i]=deepcopy (O[i]); }        returnN; } Else if(o instanceof Object) {varn = {}         for(varIincho) {n[i]=deepcopy (O[i]); }        returnN; } Else {        returno; }}
JavaScript shallow copy deep copy detailed