Global values

vi.spyOn() is a great way to mock and control global methods. However, when your code depends on global values, you need to employ a different approach.

In this exercise, we are testing the toAbsoluteUrl() function that looks like this:

/**
 * Returns absolute URL from the given URL.
 */
export function toAbsoluteUrl(url: string): string {
  return new URL(url, location.href).href
}

This is a browser-only function which purpose is to ensure the url we provided to it is returned as an absolute URL. If the url is absolute from the start, it's returned as-is. But if it is a relative URL (i.e. a pathname), it must be resolved against the current location.href.

Because of the dependency on location, we will be testing the toAbsoluteUrl() function in the happy-dom environment, which polyfills the global location object.

import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    globals: true,
    environment: 'happy-dom',
  },
})

By default, location.href in HappyDOM is set to http://localhost:3000/. However, for our new test to comply with the Golden Rule of Assertions, the value of the location.href must be set on the test's level. Otherwise, a change in Vitest configuration can result in different absolute URLs being produced, thus failing the test prematurely.

Moreover, bringing the actual location.href value to the test level will give us more control over different URL-related scenarios (e.g. IPv4 vs IPv6 URLs).

For that, we are going to use the vi.stubGlobal() utility.

👨‍💼 In this exercise, use the vi.stubGlobal API to mock the value of the global location object in the

to-absolute-url.test.ts

test suite. Verify your solution by running npm test.

🦉 Note that location inherits from URL, which means it can be partially mocked by using a URL instance as its value.

04. Globals/02. Global values (💪 problem)

Global values