This content originally appeared on DEV Community and was authored by AmanGupta1703
What is a Callstack?
- It is part of the JavaScript engine.
- A part of the JavaScript engine that keeps track of function calls.
- It is a data structure that operates on a LIFO (Last-In-First-Out) basis to remove an execution context from the Call Stack.
- - The first item pushed to the stack is the Global Execution Context. Each time a function is invoked, a new Function Execution Context is added (pushed) on top.
- Once a function completes, its context is popped off the stack.
What is an Execution Context?
- It is the environment in which JavaScript code is evaluated and executed.
-
It goes through two main phases:
- Creation Phase
- Execution Phase
The engine scans the code and allocates memory for variables and functions.
Functions are hoisted with their full definitions.
Variables declared with
varare hoisted and initialised withundefined.Variables declared with
letandconstare hoisted but remain uninitialized — they are in the Temporal Dead Zone (TDZ).Primitive values are stored in the Call Stack; reference values (like objects) are stored in the Heap.
2. Execution Phase
- The code is executed line by line.
- Variables declared with
var,let, andconstare assigned their actual values. - Accessing a
letorconstvariable before its declaration results in a ReferenceError due to the TDZ.
Temporal Dead Zone (TDZ)
- The TDZ for a
letorconstvariable starts at the beginning of its scope and ends when the variable is declared. - Accessing the variable in this zone will throw a ReferenceError.
This content originally appeared on DEV Community and was authored by AmanGupta1703
AmanGupta1703 | Sciencx (2025-06-26T13:33:52+00:00) Call Stack and Execution Context. Retrieved from https://www.scien.cx/2025/06/26/call-stack-and-execution-context/
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