Hello, developers today I will dive into the JavaScript functions. Let's start.....

In JavaScript function is one kind of non-primitive data type. The function is also one kind of object in JavaScript because in JavaScript all non-primitive data types are one kind of object.
A JavaScript function is a block of code designed to perform a particular task. When we use the same logic randomly in our code then we often use function for it.

Function
In JavaScript, we can define a function using the keyword function. A function has the function keyword, followed by aq name and a parenthesis.
The code to be excited by the function is placed inside curly braces {}. A JavaScript function is executed when something invokes it or calls it.

function add(num1,num2){
  let num3 = num1+num2;
  console.log(num3) //output is 13
}
add(8,5)//function call 

Function return
When JavaScript reaches a return statement the function will stop executing. When a function is invoked or called it will execute after finding the return it will return the value to the caller.
When a function does not return anything it will return undefined implicitly and come out from the function

function myCall(){
console.log("hello Bangladesh")//output is hello Bangladesh
}
let x= myCall();
console.log(x) //output is undefined

Function declaration and function expression
A function declarations means the normal function declaration like

function sleep(){
console.log("I am sleeping")
}
sleep()// output is I am sleeping

But function expression is a bit different. When a function is stored in a variable and called with a variable name is called a function expression

const a = function(){
console.log("Hello Bangladesh")
}
a() // output is Hello Bangladesh

This function is also called an anonymous function.

Function hoisting:
Hoisting is a JavaScript behavior of moving declaration on the top of the current scope. When a function is called before it is declared using the JavaScript hoisting method hosited the function at the top of the function call as a result it does not give any error.

add(8,5)//function call 
function add(num1,num2){
  let num3 = num1+num2;
  console.log(num3) //output is 13
}

But remember function defined using an expression are not hoisted and give an error

add(8,5)//function call 
const add = function(num1,num2){
  let num3 = num1+num2;
  console.log(num3) //give an error
}

Self-invoke functions:

When a function calls itself then it is called self invoke the function
(function(){
console.log("Hello Bangladesh");
})();

Function Parameters:
When parameters are more than arguments we passed then extra parameters will set value undefined.

function add(num1,num2){
  num3 =num1* num2 // here num1 is 8 ,num2 is undefined
  console.log(num3) //output is NaN
}
add(8,5)