How to mock windowlocationhref with Jest Vuejs

Ensuring robust and reliable unit tests for your Vue.js applications often involves tackling tricky browser-specific APIs. One common challenge developers face is precisely how to mock window.location.href with Jest + Vuejs when testing components that trigger navigation or redirection. Directly manipulating window.location during a test can lead to unpredictable behavior, test isolation issues, or even crashes, especially in a Node.js-based test environment like Jest’s jsdom. This article will guide you through effective strategies to cleanly mock window.location.href, allowing you to write stable, maintainable unit tests for your Vue components. We’ll explore fundamental Jest mocking techniques, integrate them seamlessly with Vue Test Utils, and discuss best practices to ensure your navigation logic is thoroughly validated without unintended side effects.

Understanding window.location.href and Jest’s Environment

The window.location object is a fundamental part of the browser’s Document Object Model (DOM), providing information about the current URL and methods for navigation. Its href property, specifically, represents the entire URL of the current page. When a Vue component, or any JavaScript code, assigns a new value to window.location.href, the browser typically performs a navigation action, redirecting the user to the new URL. This behavior is perfectly normal in a live browser environment but becomes problematic in a unit testing context.

Jest tests, by default, run in a Node.js environment, which simulates a browser using a library called jsdom. While jsdom provides a remarkably good approximation of the DOM, it’s not a full browser. It lacks many browser-specific APIs and behaviors, particularly those related to actual navigation, rendering, or network requests. Attempting to change window.location.href directly within a jsdom environment won’t trigger a real browser redirect. Instead, it might throw errors, silently fail, or modify the jsdom’s window.location object in a way that doesn’t truly reflect browser navigation, making assertions unreliable.

The Challenge of Browser APIs in Node.js

The core issue stems from the fact that window.location.href is an imperative browser API designed to interact with the browser’s navigation engine. In a Node.js unit test, there’s no actual browser engine to perform this navigation. Therefore, when your Vue component’s method tries to assign a value to window.location.href, Jest needs a way to intercept this assignment and allow you to assert that it happened correctly, without actually triggering a navigation that doesn’t exist in the test environment. This is where Jest’s powerful mocking capabilities become essential.

To effectively mock window.location.href in your Jest tests, you need to prevent the actual assignment from happening and instead record the intended URL. Jest offers robust tools for this, primarily Object.defineProperty and jest.spyOn. These methods allow you to control or observe how properties of global objects, like window.location, are accessed or modified during your tests. Understanding their nuances is key to implementing reliable navigation unit testing.

Using Object.defineProperty

Object.defineProperty is a JavaScript native method that allows you to define new properties on an object, or modify existing ones. Crucially, it lets you define getter and setter functions for a property. For window.location.href, this means we can override its default setter behavior to instead call a Jest mock function whenever an assignment to href occurs. This is particularly useful because window.location itself is not directly mockable using jest.spyOn on its href property as href is a primitive, not a method.

Here’s how you might use Object.defineProperty to mock window.location.href:

const assignMock = jest.fn(); delete window.location; window.location = { assign: assignMock }; // Mock the assign method if your code uses it Object.defineProperty(window, 'location', { writable: true, value: { ...window.location, // Preserve other properties if necessary href: '', // Initialize href assign: assignMock, // Keep assign mock get href() { return this._href; }, set href(url) { this._href = url; assignMock(url); // Call the mock function when href is set }, }, }); // In your test: // expect(assignMock).toHaveBeenCalledWith('/new-path'); 

This approach allows you to replace the native href setter with your own logic, which can then record the URL using a jest.fn(). Remember to clean up your mocks using beforeEach and afterEach to ensure test isolation.

Leveraging jest.spyOn

While Object.defineProperty is powerful for properties, jest.spyOn is ideal for mocking methods. If your Vue component uses window.location.assign() or window.location.replace() for navigation, jest.spyOn is the most straightforward way to mock these. This function creates a mock function similar to jest.fn() but also tracks calls to the original method, allowing you to restore it later.

let assignSpy; beforeEach(() => { assignSpy = jest.spyOn(window.location, 'assign').mockImplementation(() => {}); }); afterEach(() => { assignSpy.mockRestore(); // Restore original implementation after each test }); // In your test: // expect(assignSpy).toHaveBeenCalledWith('/new-path'); 

The key here is mockImplementation(() => {}), which prevents the actual navigation from occurring. For comprehensive Vue.js unit testing, it’s often a good practice to mock both href (if directly assigned) and methods like assign or replace to cover all potential navigation paths in your application.

Implementing Mocks in Vue.js Components with Vue Test Utils

When you’re unit testing Vue components, Vue Test Utils is your go-to library. Integrating your window.location.href mocks with Vue Test Utils involves setting up the mock before mounting your component and then asserting against the mock’s call history. This ensures that when your component’s methods trigger navigation, the test environment correctly captures these attempts without actual redirects.

Setting Up Your Test File

The mocking setup should typically occur in a beforeEach block of your test file to ensure that each test starts with a clean and isolated mock. This prevents test pollution where one test’s mock state affects another. Here’s a common pattern:

import { mount } from '@vue/test-
<b>Question & Answer : </b><br></br><p>Currently, I am implementing unit tests for my project and there is a file that contains window.location.href.</p> <p>I want to mock this to test and here is my sample code:</p> it("method A should work correctly", () => { const url = "http://dummy.com"; Object.defineProperty(window.location, "href", { value: url, writable: true }); const data = { id: "123", name: null }; window.location.href = url; wrapper.vm.methodA(data); expect(window.location.href).toEqual(url); });  <p>But I get this error:</p> TypeError: Cannot redefine property: href at Function.defineProperty (<anonymous>)  <p>How should I resolve it?</p>
<br></br><p>You can try:</p> window = Object.create(window); const url = "http://dummy.com"; Object.defineProperty(window, 'location', { value: { href: url }, writable: true // possibility to override }); expect(window.location.href).toEqual(url);  <p>Have a look at the Jest Issue for that problem:<br></br> <a href="https://github.com/facebook/jest/issues/5124" rel="noreferrer">Jest Issue</a></p>