JavaScript Basics: You should understand basic syntax, variables, data types, and operators. Learn about control structures like if-else statements, switch statements, and loops (for, while, do-while).

Functions: Learn how to define and invoke functions. Understand the difference between function declarations and function expressions. Learn about arrow functions and callbacks.

Objects and Arrays: Understand how to create and manipulate objects and arrays. Learn about methods like push, pop, shift, unshift, slice, splice, map, filter, and reduce.

JavaScript ES6 Features: ES6 brought many new features to JavaScript. Make sure you're familiar with let/const, template literals, destructuring assignment, default parameters, and the spread/rest operators.

Asynchronous JavaScript: Understand how JavaScript handles asynchronous operations. Learn about callbacks, promises, and async/await. Be familiar with AJAX and the Fetch API.

DOM Manipulation: Learn how to select, add, modify, and remove HTML elements and attributes using JavaScript. Understand how to handle events like clicks, form submissions, and keyboard events.

Error Handling: Understand how to handle errors and exceptions using try, catch, and finally.

Testing and Debugging: Learn about testing frameworks like Jest or Mocha. Know how to use console.log and debugging tools in browsers.

JavaScript Best Practices: Learn about clean code, code comments, naming conventions, and other best practices.

You should also practice coding in JavaScript as much as possible. Sites like Codecademy, FreeCodeCamp, and LeetCode have many JavaScript exercises and problems to solve. Good luck with your exam!