Mocking a useragent in javascript?

user_78182 0
Viewed 75742

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?

user-agent unit-testing javascript
15 Answers

For those here because they need to change the userAgent value in unit tests, Tyler Long's solution works, but if you want to restore the initial userAgent or change it more than once, you will probably need to set the property as configurable:

function setUserAgent(userAgent) {
    Object.defineProperty(navigator, "userAgent", { 
        get: function () { 
            return userAgent; // customized user agent
        },
        configurable: true
    });
}

// Now in your setup phase:
// Keep the initial value
var initialUserAgent = navigator.userAgent;
setUserAgent('foo');

// In your tearDown:
// Restore the initial value
setUserAgent(initialUserAgent);

Otherwise you might run into a TypeError: Cannot redefine property error. Works for me on Chrome Headless.

user_52759090

For those trying to do the same thing in TypeScript here's the solution:

(<any>navigator)['__defineGetter__']('userAgent', function(){
    return 'foo';
});

navigator.userAgent; // 'foo'

Or same thing for language:

(<any>navigator)['__defineGetter__']('language', function(){
    return 'de-DE';
});
user_34462550

Late to this topic but for Karma + Jasmin and Typescript and want to set the userAgent property this will do it: 

describe('should validate YYYY-MM-dd format only on IE browser', () => {
    // this validator has a specific condition to work only in IE11 and down
    (window as any).navigator.__defineGetter__('userAgent', function () {
      return 'MSIE';
    });

...
// rest of the test

});

This article helped: https://www.codeproject.com/Tips/1036762/Mocking-userAgent-with-JavaScript

user_69998570

Try this it worked for me without lint issues

Object.defineProperty(global.navigator, 'userAgent', { get: () => 'iPhone' });
user_72516380
Related