JavaScript Developer I is the Salesforce certification that tests JavaScript itself. Most of it is the language as it runs in any browser or in Node.js, which is exactly what Lightning Web Components are built on. If you write components, it rewards the understanding that makes them easier to debug.
What to learn
Fundamentals
Types and type coercion, let, const and var and how their scope differs, functions, closures and this. Many tricky questions come down to what a short piece of code prints.
Classes and modules
Prototypes and the class syntax built on them, inheritance, and ES modules with import and export.
Asynchronous JavaScript and the browser
The event loop, callbacks, promises and async/await, and how errors travel through them. In the browser: the DOM, events, and how events bubble and can be stopped.
Node.js, testing and tooling
Running JavaScript outside the browser, npm packages, and writing unit tests for your code. A working knowledge of TypeScript helps too.
Advanced topics
Working with arrays and objects fluently, error handling, and writing code that stays readable as it grows.
How to study it
- Predict, then run. For each concept, write a few lines, guess the output, then run them in the browser console or Node.js.
- Master the event loop. Order-of-output questions with timers and promises are common and very learnable.
- Build a small component. A Lightning Web Component that loads data and handles events ties the syllabus together.
Check the official requirements
Salesforce sets what earns this credential, and it can include more than the multiple-choice exam. Read the current requirements and exam guide on Trailhead before you plan your date.
How Arkton helps
The JavaScript Developer I course has 21 lessons with labs and exam preparation, about 21 hours of material. It pairs well with Platform Developer I, which covers the Apex side.