This content originally appeared on DEV Community and was authored by tanishparashar
How JavaScript Works
JavaScript operates in a single-threaded environment, meaning it executes one task at a time. It handles the execution of code in Execution Contexts (EC), which can be either Global or Functional.
Global Execution Context (GEC)
Created when the code file is loaded.
The GEC is responsible for setting up the global object (in browsers, it's window) and the this keyword.
All variables and functions declared in the global scope are stored in the Global EC.
Execution Context Phases
Memory Creation Phase:
During the memory phase, JavaScript allocates memory for variables and functions.
Variables are assigned the value undefined initially, while functions are stored in memory with their full definition.Execution Phase:
After the memory allocation phase, JavaScript starts executing the code line by line.
Variables are assigned actual values and functions are executed.
Functional Execution Context (FEC)
Whenever a function is invoked, JavaScript creates a new Execution Context specifically for that function.
Execution context for each function has two phases:
Memory Phase: Memory is allocated to the local variables, and functions inside the function.
Execution Phase: The function body is executed, and variables get their actual values.
After execution, the function's execution context is destroyed, freeing up memory.
Return Statements
Once a function reaches a return statement, the function immediately exits, and its execution context is removed from the Call Stack. Any code written after a return statement won't execute.
The Call Stack
JavaScript uses the Call Stack to manage execution contexts.
LIFO (Last In, First Out) concept is used:
When a function is called, its execution context is placed on top of the stack.
Once the function completes (or reaches return), its execution context is popped off the stack.
JavaScript is Single-Threaded
Single-threaded means JavaScript can only perform one operation at a time but still it can perform asynchronous operations isn't that interesting in my next post we will discuss about this amazing functionality of JavaScript.
This content originally appeared on DEV Community and was authored by tanishparashar
tanishparashar | Sciencx (2024-09-18T05:04:52+00:00) How JS works behind the scenes?. Retrieved from https://www.scien.cx/2024/09/18/how-js-works-behind-the-scenes/
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