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 function, you're just reassigning the parameter of the function. That has no effect on the passed data.

In the second, you're actually mutating the passed array via the call to pop.

Think of it this way: in

var a = 1
a = 2

Is the 1 modified in any way? No, the reference a that was pointing to it was just changed.