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How do I test JavaScript code with Jest?

Asked on Aug 30, 2025

Answer

Jest is a popular testing framework for JavaScript, especially for applications built with React. It allows you to write tests with an easy-to-use API.

<!-- BEGIN COPY / PASTE -->
        // Example function to test
        function add(a, b) {
            return a + b;
        }

        // Jest test case
        test('adds 1 + 2 to equal 3', () => {
            expect(add(1, 2)).toBe(3);
        });
        <!-- END COPY / PASTE -->

Additional Comment:

Install Jest using npm with the command: "npm install --save-dev jest".
Create a JavaScript file with the function you want to test, e.g., "add.js".
Create a test file, e.g., "add.test.js", and include the test code as shown above.
Run your tests using the command: "npx jest".

Jest automatically finds files with ".test.js" or ".spec.js" extensions.
Use "expect" to define assertions and "toBe" to check for equality.

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Ask any question about JavaScript here... and get an instant response.

How do I test JavaScript code with Jest?

Asked on Aug 30, 2025

Answer

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