What is JavaScript?

JavaScript is a dynamically typed, high-level language that is both interpreted and just-in-time (JIT) compiled. It typically runs in the V8 engine—a high-performance engine written in C++ that powers Chrome and Node.js. V8 compiles JavaScript to native machine code before execution, which helps achieve fast performance.

JavaScript follows the ECMAScript standard, which defines how the language works. Major updates like ES6 (ECMAScript 2015) introduced modern features (such as let, const, arrow functions, and classes which we'll learn about in this tutorial). Since Vite uses JavaScript modules by default, your code will run in "strict mode", which catches more errors and aligns with TypeScript’s behavior.

In this part, we'll explore key JavaScript language features most relevant to this course. Later we'll see how TypeScript enhances JavaScript with type annotations and other features that improve code quality and maintainability.