How to maintain parent variable value in javascript [duplicate]

Question

I need one clarification java script. I used two variables in my program. I stored particular array in first variable and again create one variable. I have stored second variable value in first variable.Then I pushed one vale in second variable... If i print first variable means second variable vale displayed.. My expectation is first variable value don't want to change..

 // first variable
 var test = ["a","b","c"];  

// second variable
var arr = test;
arr.unshift("d");

// second variable print
console.log(arr);  // ["a","b","c","d"]

// First variable print
    console.log(test); // ["a","b","c","d"]

// I want to maintain first original value
// Expectation result  
 console.log(test); // ["a","b","c"]

I need maintain original value in first variable..What I do?

Answer 1

You can use the spread operator (check browser capability)

var arr = [...test];

 // first variable
 var test = ["a","b","c"];  

// second variable
var arr = [...test];
arr.push("d");

// second variable print
console.log(arr);  // ["a","b","c","d"]

// First variable print
    console.log(test); // ["a","b","c","d"]

// I want to maintain first original value
// Expectation result  
 console.log(test); // ["a","b","c"]