unit testing - Is it possible to mock document.cookie in JavaScript?

Question

document.cookie is like a string, but it is not a string. To quote the example from the Mozilla doc:

document.cookie = "name=oeschger";
document.cookie = "favorite_food=tripe";
alert(document.cookie);
// displays: name=oeschger;favorite_food=tripe

If you tried to make a mock cookie using only a string, you would not get the same results:

var mockCookie = "";
mockCookie = "name=oeschger";
mockCookie = "favorite_food=tripe";
alert(mockCookie);
// displays: favorite_food=tripe

So, if you wanted to unit test a module that operates on the cookie, and if you wanted to use a mock cookie for those tests, could you? How?

Answer 1

You could create an object with a cookie setter and getter. Here is a very simple implementation:

var mock = {
    value_: '', 

    get cookie() {
        return this.value_;
    },

    set cookie(value) {
        this.value_ += value + ';';
    }
};

Might not work in all browsers though (especially IE). Update: It only works in browsers supporting ECMAScript 5!

More about getter and setters.

mock.cookie = "name=oeschger";
mock.cookie = "favorite_food=tripe";
alert(mock.cookie);
// displays: name=oeschger;favorite_food=tripe;

DEMO