Execution Context in JavaScript
- Everything in JavaScript happens inside an execution context.
- Think of an execution context as a big box or container where the entire JavaScript code runs.
- The execution context has two main components:
- Memory Component
- Code Component
1. Memory Component
- This is where all variables and functions are stored as key-value pairs.
- The memory component is also called the variable environment.
2. Code Component
- This is where the code is executed, one line at a time.
- The code component is also known as the thread of execution.
- The whole code is executed one line at a time.
Visual Representation: Execution Context
| Memory (Variable Environment) | Code (Thread of Execution) |
|---|---|
| key : value | ... |
| a : 10 | .... |
| fn : | ..... |
- Memory: Stores variables and functions as key-value pairs.
- Code: Executes code one line at a time.
Memory is also called the Variable Environment. Code is also known as the Thread of Execution.
Is JavaScript Synchronous or Asynchronous?
JavaScript is a synchronous, single-threaded language by default.
- It executes one command at a time, in a specific order.
- Each line of code runs only after the previous line has finished.
- This means JavaScript moves to the next line only when the current line is done.
Note
While JavaScript itself is synchronous, it can handle asynchronous operations (like callbacks, promises, and async/await) using its event loop and browser APIs. These features allow JavaScript to perform non-blocking operations, but the core execution model remains single-threaded and synchronous.