I have seen many developers struggle with testing and debugging their code. However, it doesn't have to be a painful experience! With the right practices in place, you can easily test and debug your JavaScript code without any headaches.

Let us discuss the 10 best practices for JavaScript testing and debugging that every beginner developer should know.

1. Use a testing framework

One of the common practices for testing in JavaScript is to use a testing framework. There are many popular testing frameworks out there, such as Jest, Mocha, and Jasmine, that can help you write tests quickly and easily. These frameworks provide a set of tools and APIs to create tests, assertions, and test suites.
example using Jest to test a function

function add(a, b) {
  return a + b;
}

test('adds 1 + 2 to equal 3', () => {
  expect(add(1, 2)).toBe(3);
});

2. Write unit tests

Unit tests are an essential part of testing JavaScript code. These tests focus on testing small, isolated pieces of code, such as individual functions or methods. Writing unit tests ensures that your code is functioning as expected and helps catch bugs early in the development process.
example of a unit test using Mocha:

describe('Array', function() {
  describe('#indexOf()', function() {
    it('should return -1 when the value is not present', function() {
      assert.equal([1,2,3].indexOf(4), -1);
    });
  });
});

3. Test edge cases

Testing edge cases is an essential part of testing JavaScript code. Edge cases are the scenarios that are unlikely to happen but still need to be tested.
These can include negative scenarios, boundary conditions, and uncommon scenarios. When you test edge cases, you can ensure that your code is robust and can handle unexpected inputs or scenarios.

example of testing an edge case:

function divide(a, b) {
  if (b === 0) {
    throw new Error('Cannot divide by zero');
  }
  return a / b;
}

test('divides two numbers', () => {
  expect(divide(6, 2)).toBe(3);
});

test('throws error when dividing by zero', () => {
  expect(() => divide(6, 0)).toThrow('Cannot divide by zero');
});

4. Use descriptive test names

Descriptive test names help you and also other developers understand what the test is testing without having to read the test code.
example

test('adds two numbers', () => {
  expect(add(1, 2)).toBe(3);
});

test('returns -1 when the value is not present in the array', () => {
  expect([1,2,3].indexOf(4)).toBe(-1);
});

5. Test one thing at a time

When you test multiple things at once, it becomes harder to identify the cause of failures or bugs. Testing one thing at a time makes your tests easier to read and understand.

example of testing one thing at a time:

test('adds two positive numbers', () => {
  expect(add(1, 2)).toBe(3);
});

test('adds two negative numbers', () => {
  expect(add(-1, -2)).toBe(-3);
});

6. Use debugging tools

Using debugging tools is an important practice for debugging your JavaScript code. Debugging tools can help you identify and fix errors in your code quickly and efficiently. Some popular debugging tools for JavaScript include Chrome DevTools, Node.js Debugger, and Visual Studio Code Debugger.

You can use Chrome DevTools to debug a function direct from the browser as in this example:

function add(a, b) {
  return a + b;
}

console.log(add(1, 2));

When you add a console.log statement, we can see the result of the function in the console. We can also use the DevTools debugger to step through the code and identify any errors or issues which brings us to the next best practice

7. Use console.log statements

Console.log statements allow you to print values and messages to the console, which can help you understand the behavior of your code.
example:

function add(a, b) {
  console.log(`Adding ${a} and ${b}`);
  return a + b;
}

console.log(add(1, 2));

8. Follow the AAA pattern

The AAA pattern (Arrange, Act, Assert) is a popular pattern for organizing unit tests. The AAA pattern separates tests into three parts: arranging the data, acting on the data, and asserting the result.

Following the AAA pattern makes your tests more organized and easier to understand. Example:

test('adds two numbers', () => {
  // Arrange
  const a = 1;
  const b = 2;

  // Act
  const result = add(a, b);

  // Assert
  expect(result).toBe(3);
});

9. Refactor your code

Refactoring involves making changes to your code to improve its readability, maintainability, and performance. When you refactor your code, you should also update your tests to ensure that they still pass.

example below show how you can refactor a function:

// Original function
function add(a, b) {
  return a + b;
}

// Refactored function
function add(...numbers) {
  return numbers.reduce((sum, num) => sum + num, 0);
}

10. Test often

By testing often, you can catch bugs early in the development process, which can save you time and effort in the long run. You should also test your code whenever you make changes to ensure that everything still works as expected.

test('adds two numbers', () => {
  expect(add(1, 2)).toBe(3);
});

test('adds three numbers', () => {
  expect(add(1, 2, 3)).toBe(6);
});

test('adds four numbers', () => {
  expect(add(1, 2, 3, 4)).toBe(10);
});

These practices will help you write better code, catch bugs early, and save time and effort. You can become more efficient and effective at writing code and remember to test often, use descriptive test names, and refactor your code to maintain its quality.

Let me know which is your favorite and how else you implement best practices in Javascript.

Happy coding!