Question

I’m learning JS here, and have a question regarding primitive values when passed in as arguments. Say I have a simple function:

var first = 5;
var second = 6;

function func(){
    first+=second;
}
func();
alert(first); //outputs 11

So in this case the value of first becomes 11.. But if I try it by passing in first as an argument to the function, first remains 5..

var first = 5;
var second = 6;

function func(first){
    first+=second;
}
func(first);
alert(first); //outputs 5

wondering if someone could explain this to me.

Answer 1

It happens because when you call function first() with no arguments, it uses the global var “first”. But when you call function first(first), you says to browser that now first is a local variable (only inside the function) and it doesn’t make any changes to the global var first. Here’s the code:

var first = 5;
var second = 6;
function func(first){
    first += second; //Local var "first" + global var "second"
    alert(first); //Local var, outputs 11
}
func(first);
alert(first); //Global var, outputs 5