XHR testing in Jest

Question

I want to test AJAX methods (vanilla XHR) and I can\'t find the way to do it with Jest framework. I found mock-ajax.js for Jasmine, the problem

Answer 1

Here's a function that will create a XMLHttpRequest mock and install it into window for you.

const mockXMLHttpRequest = () => {
  const mock = {
    open: jest.fn(),
    addEventListener: jest.fn(),
    setRequestHeader: jest.fn(),
    send: jest.fn(),
    getResponseHeader: jest.fn(),

    upload: {
      addEventListener: jest.fn(),
    },
  };

  window.XMLHttpRequest = jest.fn(() => mock);

  return mock;
};

Which you can then use in a test like so:

const mock = mockXMLHttpRequest();

// Get the upload progress callback
// This assumes you attach your listeners in a stable order
expect(mock.upload.addEventListener).toHaveBeenCalledTimes(1);
const [[, progress]] = mock.upload.addEventListener.mock.calls;

// Get the load callback
expect(mock.addEventListener).toHaveBeenCalledTimes(1);
const [[, load]] = mock.addEventListener.mock.calls;

expect(mock.open).toHaveBeenCalled();
expect(mock.send).toHaveBeenCalled();

// Fire a progress event
progress({ loaded: 12, total: 100 });

// ...

mock.status = 201;
mock.getResponseHeader.mockReturnValue('application/json');
mock.response = JSON.stringify({ id: 111 });

// Fire a load event
load();

// ...