We would have studied in maths that a function is something where it takes some gebrish and return some other gebrish.

Okay!! Let's Start from Beginning.

When we write a programs, we often repeat the same logic many times for example i want to add two number how would a noob will do the same thing?

console.log(5 + 3) Output ->8
console.log(10 + 2) Output ->12 
console.log(7 + 6) Output -> 13

Here we are doing addition again and again. what if i write something and i give it my two number and by doing some magic it returns me the ans without of me adding + + + again and again for all operation. That magic is called function

A function is a reusable block of code that performs a task.

Write it once and use it many times.

function add(a, b){
    return a + b;
}

// This is the one time we need to define the function 
// Basically making a function

But wait how to use it?

console.log(add(2,3)) // calling the function and printing it

so using of a function is calling calling of function and making of function is called declaration.

Now i can re use it again and again, let's see the whole code and dry run!

function add(a,b){
     console.log(a+b);
}

add(2,3);
add(2,5);

Output

5
7

Now we know some sort of function!

Function Expression

A function can also be stored inside a variable.

Example:

let add = function(a, b){
    return a + b;
}

console.log(add(5,3))

Output

8

Here the function does not have its own name.

It is stored inside the variable add.

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Declaration vs Expression

Side by side comparison.

Function Declaration

function greet(){
    console.log("Hello")
}

Function Expression

let greet = function(){
    console.log("Hello")
}

Both create functions, but the way they behave in memory is slightly different.

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Basic Idea of Hoisting

JavaScript moves some declarations to the top of the scope during execution.
This behavior is called hoisting.

---

Function Declaration Hoisting

This works:

greet()
function greet(){
    console.log("Hello")
}

Output:

Hello

Even though we called the function before defining it, it still works.

Because function declarations are hoisted.

---

Function Expression Hoisting

This does not work:

greet()
let greet = function(){
    console.log("Hello")
}

Error occurs because the variable greet is not ready yet.

Function expressions behave like normal variables, so they are not available before assignment.