# 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

```javascript
returnType functionName(parameterType parameterName, ...);  
```

### **Key Points:**

1. **Declares function before use** – Useful in compiled languages like C.
    
2. **Specifies function signature** – Includes name, return type, and parameters.
    
3. **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.

```javascript
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.