How are variables passed to functions in JavaScript?

gistfile1.txt

/*
 * JavaScript variables are always passed by value. This works as you
 * expect it to when you pass primitives to functions.
*/

function add1(x) {
  // We get passed a copy of x's value -- which is a number -- so we can't
  // update the original variable's value
  x++;
}

var x = 0;
add1(x);
console.log("x is", x); // "x is 0"

/*
 * What happens when we pass an object? JavaScript still passes by value, but
 * the value we're passing is a *reference* to the object.
*/

function setName(obj) {
  // We get passed a copy of obj's value -- which is a reference --  so we can
  // still update its properties
  obj.name = "Nick";
}

var obj = {};
setName(obj);

console.log("obj.name is", obj.name); // "obj.name is Nick"

/*
 * Further exploration: What about boxed objects?
*/