# JavaScript : Function Declaration vs Function Expression

Lets understand `function` as var can store the value same as function store the single or multiple line of code which we can use where we need.

> Instead of writing the same code again and again, you wrap it inside a function and call it whenever needed.

like:

```javascript
function add(a, b) {// syntax for creating function with vars 
  return a + b; // now code for adding 2 numbers
}
// now we call function with values which we need to perform action
console.log(add(2, 3)); // 5
// add is function and 2,3 are the values of 'a' and 'b' which functions required
```

as we see above this is f`unction declaration`,

### Function Type

*   function declartion
    
*   function expression
    

```javascript
//function declation as we already seen lets discuss both again
// Function Declaration
function add(a, b) {
  return a + b;
}

// Function Expression just same as above but it store in var
const addExp = function(a, b) {
  return a + b;
};

console.log(add(2, 3));     // 5 // calling way is the same 
console.log(addExp(2, 3));  // 5 // for function declation and expression
```

### Hoisting

hosting is the issue when fuction call before creation.

*   `function declaration` never create this issue
    
*   `function expression` has the issue of hoisting because it store it the variable
    

```javascript
console.log(multiply(2, 5)); // ✅ works

console.log(multiplyExp(2, 5)); // ❌ error

function multiply(a, b) {
  return a * b;
}

const multiplyExp = function(a, b) {
  return a * b;
};
// both works here
console.log(multiply(2, 5)); // ✅ works

console.log(multiplyExp(2, 5)); //✅ works
```

> Hoisting means JavaScript **moves declarations to the top**

| Feature | Function Declaration | Function Expression |
| --- | --- | --- |
| Syntax | `function name()` | `const name = function()` |
| Hoisting | ✅ Yes | ❌ No |
| Use Before Definition | ✅ Works | ❌ Error |

### Summary

Functions is block of code which can process the different values which can be used in multple places which different values.

### Use Function Declaration:

*   When you want to define reusable functions early
    
*   When you may call it before writing it
    
*   simple, hoisted, beginner-friendly
    

### Use Function Expression:

*   When assigning functions to variables
    
*   When using functions as values (common in modern JS)
    
*   flexible, used more in modern JavaScript