Function Declaration vs Function Expression

What is Function Declaration ?

A Function Declaration is a way of defining a function in programming . It tells the compiler function name , return type and parameter before it is used It allows the function to be called before its actual definition in the code

Function declaration Syntax in C/C++/JS

returnType functionName(parameterType parameterName, ...);

Key Points:

Declares function before use – Useful in compiled languages like C.
Specifies function signature – Includes name, return type, and parameters.
Allows separation of declaration and definition – Common in header files for C/C++.

What is Function Expression ?

A function expression is a way of defining a function inside an expression and assigning it to a variable. Unlike function declarations, function expressions do not get hoisted, meaning they cannot be called before they are defined.

const variableName = function(parameters) {
    // Function body
    return something;
};

Key Differences Between Function Declarations and Expressions

Feature	Function Declaration	Function Expression
Hoisting	✅ Yes (can be called before declaration)	❌ No (must be declared first)
Syntax	`function myFunc() {}`	`const myFunc = function() {};`
Naming	Required	Optional (anonymous or named)
Use Cases	Global functions, reusable code	Dynamic functions, callbacks, event handlers
Stack Trace Name	Clearly named in errors	May be anonymous

When to Use Each?

Use Function Declarations when:

✅ You need to call the function before it's defined.
✅ The function is meant to be reusable throughout the script.
✅ Readability and stack trace clarity are important.

Use Function Expressions when:

✅ You need to define functions dynamically inside expressions.
✅ You’re working with callbacks or immediately invoked function expressions (IIFE).
✅ You want to control when and how a function is executed.