JavaScript Unit Testing: How to Write and Test Your First Functions

How do you know if your JavaScript code actually works under every scenario? Writing manual console logs to check your functions is slow, repetitive, and prone to missing critical bugs. This text-based course guides you through the foundational concepts of unit testing in JavaScript. You will learn how to write clean, testable functions—starting with a practical vowels counter—and verify their correctness using structured assertions. What you'll learn: - Learn the core principles of unit testing, assertions, and the test-driven development mindset. - Understand how to structure tests using the standard Arrange-Act-Assert pattern. - Build clean, pure JavaScript functions designed specifically for easy testability. - Apply modern assertion syntax and matcher functions to verify expected outputs against actual results. - Practice writing test suites that cover edge cases, empty inputs, and unexpected data types. You will start by exploring basic testing terminology and the setup of a test file. From there, you will step through writing a practical string manipulation function and crafting its corresponding unit tests to handle various scenarios. This course is designed for beginner JavaScript developers who want to write more reliable code and understand the fundamentals of software testing. No prior testing experience is required. Start reading today to build confidence in your code through automated testing.