Javascript (mainly) pass-by-value

reference_by_value.js

// More explicit example of 
// http://stackoverflow.com/questions/518000/is-javascript-a-pass-by-reference-or-pass-by-value-language
//
// When you change the `item` property of the object referenced by `obj1`, you are changing the value 
// of the `item` property that was originally set to 'unchanged'. When you assign `obj2` a value of 
// {item: 'changed'} you are changing the reference to a new object. This object immediately goes out 
// of scope when the function exits.

function changeStuff(_num, _obj1, _obj2) {
    _num = _num * 10;
    _obj1.item = 'changed';
    _obj2 = {item: 'changed'};
}

var num = 10,
    obj1 = {},
    obj2 = {};

obj1.item = 'unchanged';
obj2.item = 'unchanged';

changeStuff(num, obj1, obj2);

console.log(num);         // 10
console.log(obj1.item);   // "changed"
console.log(obj2.item);   // "unchanged"