Javascript passing arrays to functions by value, leaving original array unaltered

Question

I\'ve read many answers here relating to \'by value\' and \'by reference\' passing for sending arrays to javascript functions. I am however having a problem sending an array

Answer 1

If you need to do this with an object, try this fancy trick...

MY_NEW_OBJECT = JSON.parse(JSON.stringify(MY_OBJECT));

Answer 2

With ES6, you can use the spread syntax and destructuring to perform a shallow copy directly in the argument list, allowing you to keep the original array unaltered.

See example below:

const arr = [1, 2, 3, 4, 5];

function timesTen([...arr]) { // [...arr] shallow copy the array
  for(let i = 0; i < arr.length; i++) {
    arr[i] *= 10; // this would usually change the reference
  }
  return arr;
}

console.log(timesTen(arr));
console.log(arr); // unaltered

Answer 3

var aArray = [0.0, 1.0, 2.0];
var aArrayCopy = aArray.concat();
aArrayCopy[0] = "A changed value.";
console.log("aArray: "+aArray[0]+", "+aArray[1]+", "+aArray[2]);
console.log("aArrayCopy: "+aArrayCopy[0]+", "+aArrayCopy[1]+", "+aArrayCopy[2]);

This answer has been edited. Initially I put forth that the new operator handled the solution, but soon afterward recognized that error. Instead, I opted to use the concat() method to create a copy. The original answer did not show the entire array, so the error was inadvertently concealed. The new output shown below will prove that this answer works as expected.

aArray: 0, 1, 2
aArrayCopy: A changed value., 1, 2