call_stack.txt

JavaScript works in three phases during execution:

1. Global Execution Context (GEC)
The Global Execution Context is created when the JavaScript engine starts running a script.
The this keyword:
In a browser, this refers to the global window object.
In Node.js, this refers to an empty object {}.
It is the default context in which code is executed unless explicitly inside a function.


2. Memory Phase (Creation Phase)
In this phase, the JavaScript engine scans the code and:
Allocates memory for variables and functions.
Variables are initialized to undefined.
Functions are assigned their entire function definition.
No actual code execution happens in this phase.


3. Execution Phase
The JavaScript engine executes the code line by line.
Variables get their actual values.
Functions are executed when called, creating a new Function Execution Context (FEC).
The Function Execution Context also has two sub-phases:
Memory Phase: Reserves memory for variables and initializes them (e.g., variables to undefined and function definitions).
Execution Phase: Runs the code inside the function.

The return value of the function is sent back to the Global Execution Context.
Short and Clear Explanation


Global Execution Context (GEC): The base environment where the script starts, setting this to window (browser) or {} (Node.js).
Memory Phase: Allocates memory for variables (undefined) and functions (definitions).
Execution Phase: Executes code line-by-line. Functions create their own Function Execution Context that works like GEC but limited to the function's scope.
Each Function Execution Context completes and passes its return value back to the Global Execution Context.