functions is a piece of code that we use to reduce code repeatability

Syntax:

function function_name(parameters){
   //code to be executed
}

// calling function with custom arguments

function_name(arguments);

Spread and rest operator as parameter and arguments

//Rest
function sum(...nums){
let total=0;
for(let i of nums){
total+=nums;
}
return total;
}

console.log(sum(1,2))

console.log(sum(1,2,3,4,5))
/* we can give any numbers of arguments and ...nums will take
all the arguments and convert it to array */

//Spread
function sum(num1,num2,num3){
return num1+num2+num3;
}

const nums=[1,2,3];
console.log(sum(...nums));
/*...nums will pass array elements as arguments and
 pass the required parameters*/
/* if no. of parameters are greater than
 elements in array then it will give NaN as output */

Objects as parameter

// we write object parameter as anyobject

function handelObject(anyobject){
// to access any keyed collections
console.log(anyobject.key_name)
}

const user={
name:"aakash"
}

handelObject(user)

Arrow function (this function)

const user ={ 
  username:"aakash",
  price: 321,

   welcomeMessage: function (){
     console.log(`${this.username} , welcome to website`);
  /* this keyword refers to the context where a piece of code
such as a function's body is supposed to run */
     }
}

user.welcomeMessage();
user.username="anand";
user.welcomeMessage();

// In browser if we print this then it will give window as a object
/* we can only use this in object not in function */
 const welcome = function () {
   let user = "aakash"
   console.log(user);
}

    const welcome = function () {
   let user = "aakash"
   console.log(user);
}

Implicit and explicit return

// explicit return when we use return word
const sum = (num1,num2) => {
return num1+num2
}

//implicit return when we use parenthesis
const sum = (num1,num2) => (num1+num2)

// to return an object
({name:"aaksh"})

Immediately invoked function expression (IIFE)

(Function defination)()

(function welcome(){
    console.log("hello")})()


( () => {
   console.log("dhjv")})()
// it will provide error so use semicolom

//we can also give parameters and arguments to the function

( (parameter) => {
    // code to be executed
})(argument);

//names iife is function with name
// unnamed iife is function with without name