Javascript function not modifying array (reference?)

Question

If JavaScript passes a function argument as a reference on the original object, why can´t I modify the original array with this simple function?

var array1 = ["one"];

function change(array) {
   var array2 = ["222"];
   array = array2;
}

change(array1);

console.log(array1); // this prints ["one"] instead of ["222"]

Why sometimes objects seem to be passed as reference and in this case it´s passed as a copy?

Answer 1

Because the parameter array isn't the same as array1. They are separate variables. Note that variables are pass-by-value, for objects it's passing a copy of the reference by value. So you would need to do:

var array1 = ["one"];

array1 = change(array1);

function change(array) {
   var array2 = ["222"];
   array = array2;
   return array;  
}

console.log(array1);

Answer 2

Why sometimes objects seem to be passed as reference and in this case it´s passed as a copy?

It's not passed as a copy of the array, it's passed as a copy of the reference to the array. There is still only one array, and you can change the array in the function using that reference:

var array1 = ["one"];

function change(array) {
   array[0] = "222";
}

change(array1);

console.log(array1); // this prints ["222"]

What you can't do is to replace the array with a different array in the function. If you assign a new array to the parameter then it will point to the new array, but the variable array1 is still unchanged and points to the original array.