Mocking a useragent in javascript?

Question

I'm looking for a way to programmatically change navigator.userAgent on the fly. In my failed attempt to get an automated javascript unit tester, I gave up and attempted to begin using fireunit. Immediately, I've slammed into one of the walls of using an actual browser for javascript testing.

Specifically, I need to change navigator.userAgent to simulate a few hundred userAgent strings to ensure proper detection and coverage on a given function. navigator.userAgent is readonly, so I seem stuck! How can I mock navigator.userAgent? User Agent Switcher (plugin) can switch FF's useragent, but can I do it within javascript?

Answer 1

No, i doubt you can do it within javascript. But with Firefox's User Agent Switcher you can test whatever useragent you want, so why not just use that?

Answer 2

navigator.userAgent is a read-only string property

really dont think there is any possibility to edit it.

if ever u get to do it plz post the solution its very interesting :D

Answer 3

Try:

navigator.__defineGetter__('userAgent', function(){
    return 'foo' // customized user agent
});

navigator.userAgent; // 'foo'

Tried it in FF2 and FF3.

Answer 4

I guess I'd take a dependency injection approach. Instead of:

function myFunction() {
    var userAgent = navigator.userAgent;
    // do stuff with userAgent
}

Maybe do something like:

function myFunction(userAgent) {
    // do stuff with userAgent
}

function getUserAgent() {
    window.userAgentReal = +window.userAgentReal || 0;
    return [ navigator.userAgent ][window.userAgentReal++];
}

function getUserAgentMock() {
    window.nextUserAgentMock = +window.nextUserAgentMock || 0;
    return [
        'test user agent1',
        'test user agent2',
        'test user agent3'
    ][window.nextUserAgentMock++];
}

var userAgent;
while (userAgent = getUserAgent()) {
    myFunction(userAgent);
}

Then you can "mock out" getUserAgent() by doing:

function getUserAgentReal() { // formerly not 'Real'
    // ...
}

function getUserAgent() { // formerly 'Mock'
    // ...
}

This design still isn't completely automated (you have to manually rename the getter to perform your testing), and it adds a bunch of complexity to something as simple as operating on navigator.userAgent, and I'm not sure how you'd actually identify any bugs in myFunction, but I just figured I'd throw it out there to give you some ideas how this might be dealt with.

Maybe the idea of "dependency injection" presented here can somehow be integrated with FireUnit.