Why do some operations not alter an array that was passed to a function?

Question

Scenario 1:

var myArray = [2, 3, 4, 5];
function doStuff(arr) {
  arr = [];
}
doStuff(myArray);
console.log(myArray); // [2,3,4,5]
         


        

Answer 1

In the first case you are doing a new memory allocation while you are actually modifying the array in the second case.

Hence in the first case the value does not get modified.

For eg:

var myArrayOne = [2, 3, 4, 5];
function doStuff(arr) {
  arr = [7,8,9]; //assigining a whole new object to the copy 
}
doStuff(myArrayOne);
console.log(myArrayOne); // [2,3,4,5]

// Scenario 2
var myArrayTwo = [2, 3, 4, 5];
function doStuff(arr) {
  arr.pop(); //modifying the internals of the arr object
}
doStuff(myArrayTwo);
console.log(myArrayTwo); // [2,3,4]