Two methods for deep and shallow copies of JavaScript arrays

Here's an example:

var arr = ["One","Two","Three"];

var arrto = arr;
arrto[1] = "test";
document.writeln(" Original value of array: " + arr + "<br />");//Export: the original value of the array: One,test,Three
document.writeln(" New value of array: " + arrto + "<br />");//Export: New value of array: One,test,Three

The direct assignment like the one above is the shallow copy, and a lot of times, that's not what we want, we want the arr to be the same, right?

Method 1: slice function of js

 for array The object's slice The function,  
 Returns a segment of an array. (still an array)  
arrayObj.slice(start, [end])  
 parameter  
arrayObj  
 Will be options. a  Array  Object.   
start  
 Will be options. arrayObj  The starting element of the specified part in the.   
end  
 Optional. arrayObj  The end element of the specified part in   
 instructions  
slice  Method returns a  Array  Object that contains  arrayObj  The specified part of.  
slice  Copy the method all the way to  end  The element specified, but not included. if  start  It's negative. Let's write it as  length + start Processing, here  length  Is the length of the array. if  end  If it's negative, let's write it as  length + end  Processing, here  length  Is the length of the array. If you omit  end  , then  slice  The method will copy all the way to  arrayObj  In the end. if  end  Appear in the  start  Previously, no elements were copied into the new array. 

Example:

var arr = ["One","Two","Three"];

var arrtoo = arr.slice(0);
arrtoo[1] = "set Map";
document.writeln(" Original value of array: " + arr + "<br />");//Export: the original value of the array: One,Two,Three
document.writeln(" New value of array: " + arrtoo + "<br />");//Export: new value of the array: One,set Map,Three

Method 2: js concat method

concat()  Method is used to join two or more arrays. 
 This method does not change the existing array, but simply returns a copy of the concatenated array. 
 grammar 
arrayObject.concat(arrayX,arrayX,......,arrayX)
 instructions 
 Returns a new array. The array is passed by putting all  arrayX  Add parameters to  arrayObject  Is generated in. If you want to do  concat()  The operation takes an array as an argument, so the elements in the array are added, not the array. 
var arr = ["One","Two","Three"];

Example:

   
var arrtooo = arr.concat();
arrtooo[1] = "set Map To";
document.writeln(" Original value of array: " + arr + "<br />");//Export: the original value of the array: One,Two,Three
document.writeln(" New value of array: " + arrtooo + "<br />");//Export: New value of array: One,set Map To,Three