How can I mock a fetch request in Jest when testing async functions in JavaScript?

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How can I mock a fetch request in Jest when testing async functions in JavaScript?

Asked on Dec 19, 2025

Answer

To mock a fetch request in Jest for testing async functions, you can use Jest's built-in mocking capabilities. This allows you to simulate the behavior of the fetch API and test how your code handles the response.

<!-- BEGIN COPY / PASTE -->
        // Example async function using fetch
        async function fetchData(url) {
            const response = await fetch(url);
            const data = await response.json();
            return data;
        }

        // Jest test case
        test('fetchData returns data from API', async () => {
            // Mock the fetch function
            global.fetch = jest.fn(() =>
                Promise.resolve({
                    json: () => Promise.resolve({ key: 'value' }),
                })
            );

            const data = await fetchData('https://api.example.com/data');
            expect(data).toEqual({ key: 'value' });

            // Ensure fetch was called with the correct URL
            expect(global.fetch).toHaveBeenCalledWith('https://api.example.com/data');
        });
        <!-- END COPY / PASTE -->

Additional Comment:

The `fetchData` function is an example of an async function that uses fetch.
In the Jest test case, `global.fetch` is mocked to return a resolved promise with a JSON object.
The `expect` statements verify that the data returned by `fetchData` matches the mock data and that fetch was called with the correct URL.
This approach allows you to test how your code handles fetch responses without making actual network requests.

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How can I mock a fetch request in Jest when testing async functions in JavaScript?

Asked on Dec 19, 2025

Answer

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