Mocking `document` in jest

Question

I'm trying to write tests for my web components projects in jest. I already use babel with es2015 preset. I'm facing an issue while loading the js file. I have followed a piece of code where document object has a currentScript object. But in test context it is null. So I was thinking of mocking same. But jest.fn() is not really help in same. How can I handle this issue?

Piece of code where jest is failing.

var currentScriptElement = document._currentScript || document.currentScript;
var importDoc = currentScriptElement.ownerDocument;

Test case I have written. component.test.js

import * as Component from './sample-component.js';

describe('component test', function() {
  it('check instance', function() {
    console.log(Component);
    expect(Component).toBeDefined();
  });
});

Following is the error thrown by jest

Test suite failed to run

    TypeError: Cannot read property 'ownerDocument' of null

      at src/components/sample-component/sample-component.js:4:39

Update: As per suggestion from Andreas Köberle, I have added some global vars and tried to mock like following

__DEV__.document.currentScript = document._currentScript = {
  ownerDocument: ''
};
__DEV__.window = {
  document: __DEV__.document
}
__DEV__.document.registerElement = jest.fn();

import * as Component from './arc-sample-component.js';

describe('component test', function() {
  it('check instance', function() {
    console.log(Component);
    expect(Component).toBeDefined();
  });
});

But no luck

Update: I have tried above code without __dev__. Also by setting document as global.

Answer 1

Similar to what others have said, but instead of trying to mock the DOM yourself, just use JSDOM:

__mocks__/client.js

import { JSDOM } from "jsdom"
const dom = new JSDOM()
global.document = dom.window.document
global.window = dom.window

Then in your jest config:

"setupFiles": [
  "./__mocks__/client.js"
],

Answer 2

I have resolved this using setUpFiles property in jest. This will execute after jsdom and before each test which is perfect for me.

Set setupFiles, in Jest config, e.g.:

"setupFiles": ["<rootDir>/browserMock.js"]


// browserMock.js
Object.defineProperty(document, 'currentScript', {
  value: document.createElement('script'),
});

Ideal situation would be loading webcomponents.js to polyfill the jsdom.

Answer 3

I could resolve this same issue using global scope module on nodejs, setting document with mock of document, in my case, getElementsByClassName:

// My simple mock file
export default {
    getElementsByClassName: () => {
        return [{
            className: 'welcome'
        }]
    }
};

// Your test file
import document from './name.component.mock.js';
global.document = {
    getElementsByClassName: document.getElementsByClassName
};

Answer 4

I have been struggling with mocking document for a project I am on. I am calling document.querySelector() inside a React component and need to make sure it is working right. Ultimately this is what worked for me:

it('should test something', () => {
    const spyFunc = jest.fn();
    Object.defineProperty(global.document, 'querySelector', { value: spyFunc });
    <run some test>
    expect(spyFunc).toHaveBeenCalled()
});

Answer 5

If like me you're looking to mock document to undefined (e.g. for server side / client side tests) I was able to use object.defineProperty inside my test suites without having to use setupFiles

Example:

beforeAll(() => {
  Object.defineProperty(global, 'document', {});
})

Answer 6

If you need to define test values for properties, there is a slightly more granular approach. Each property needs to be defined individually, and it's also necessary to make the properties writeable:

Object.defineProperty(window.document, 'URL', {
  writable: true,
  value: 'someurl'
});

See: https://github.com/facebook/jest/issues/890

This worked for me using Jest 21.2.1 and Node v8.11.1