JavaScript is synchronous by default, but it also supports asynchronous behavior through mechanisms like:

• Callbacks
• Promises
• Async/Await
• Web APIs (like setTimeout, fetch, etc.)

JavaScript is both interpreted and compiled

• JavaScript is an interpreted language, meaning it can be executed line by line without a prior compilation step like C or Java.
• BUT modern engines use Just-In-Time (JIT) compilation, which means:
  • The JS code is parsed into an Abstract Syntax Tree (AST)
  • It's compiled to bytecode, then sometimes to machine code at runtime
  • This makes it much faster than purely interpreted execution

To run JS outside browser, use NodeJS

NodeJS is built on top of V8 Engine

Global Execution Context

When a JavaScript program runs, the engine creates an Execution Context. The first one it creates is the Global Execution Context (GEC).

There are two phases in the GEC:

1. Creation Phase