js | Functions |

Functions

Functions are pieces of code that we can reuse again and again in our code

Function Declaration - JavaScript Hoisting

syntax:

function functionName( ){

// code block

}

functionName()  //calling function

Example:

function msg( ){

console.log("Hii...Hello");

}

msg()  //calling function
//msg()

output:

Hii...Hello
//Hii...Hello

A function declaration defines a named function.It's hoisted,
meaning you can call it before it's defined.

Calling the function:

HOSTING

msg()  // valid  HOSTING

function msg( ){

console.log("Hii...Hello");


}

output:

Hii...Hello

Function Parameters and Arguments

syntax:

                        //input 
function functionName( parameter ){

// code block   //output

}

functionName( arguments)  //calling function

Functions can take parameters, which act as placeholders for the values
that will be passed to the function.The passing value is called an argument.

function msg( name ){

console.log("Hii...Hello" + name);

}

msg( "ranjith") ;
msg( "kumar") ;


output:

Hii...Hello ranjith

multiple parameters

function msg( name ,age){

console.log("Hii", + name +" my age"+age);

}

msg( "ranjith",25) ;
msg( "kumar",20) ;

Default Parameter

function printer(color){

console.log("print document in ${color} color");

}

//printer("blue") 
printer("blue") 

output:

document coloe blue color

//red override
function printer(color="black"){

console.log("print document in ${color} color");

}

//printer("red") 
printer( ) 

output:

//document coloe red color

document coloe black color

 Function with Return Type

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

}

 let sum = add(10,20); //variable vechu assign panni print pannrom
 console.log(sum);  //30

 //console.log(add(10,20);   check pls

 Function Expression

A function expression defines a function inside an expression.
It's not hoisted, so you can't call it before it's defined.

syntax:

    variable      keyword
let functionName=function ( ){

   //code block

}

functionName()   // calling function

Ex:

           //don't change 
 let msg = function( ){   // function() indha typelaa kandippa irukkanum

 console.log("good morning");

}

msg( ) ;  //good morning 

With Argument

//msg( "ranjith") ;   // exp not hositing

let msg = function( name ){

console.log("good morning ${name}");

}

msg( "ranjith") ;  //good morning ranjith

Function Expression with Return Type

let mul = function (a,b){
   return a*b;

};

let result = mul( 5,2 ){
console.log(result); //10

 //console.log(mul(4,7));

 Arrow Function

 Arrow functions provide a concise syntax and do not bind their own 'this'. They are not hoisted.

 syntax:  

    variable      keyword
let functionName=( ) =>{

   //code block

}

functionName()   // calling function

Example:

let evening = ( ) =>{

 console.log("good evening everyone");

}

evening ()   // good evening everyone 

With Argument

//not hoisting

let evening = ( name ) =>{

 console.log("good evening " + name);

}

evening ("ajith")   // good evening ajith

 Arrow Function with Return Type

 let sub =( a,b ) =>{
    return a - b ;
 };

  console.log( sub(10,6); // 4

Shorter Way

let sub =(a,b) => a-b;

console.log(sub(10,6)); //4

Function Calling Other Function

                       //ranjith
 function welcomeShopper(name){

 console.log(" welcome ${name} ! enjoy yoyr shopping experience")

}              //ranjith
    function main(name){

   // welcomeShopper(name); // direct calling
                   //ranjith
   let ShopperName-name;  // variableassign and after calling
                   //ranjith
   welcomeShopper(ShopperName); // calling top welcomeshopper

  };

  main("ranjith")  // welcome ranjith ! enjoy your.....

Anonymous Functions: Later on Course on Arrays

serTimeout(() => {

   console.log(" anonymous function executed");

 },2000 // 2sec delay  

 output: anonymous function executed

Scope of variables will on functions and loops

var: Function scoped.

Ex:

function demo(){
    var a =20;
    console.log(a); 

  }
demo();
console.log(a)  //error function outside calling

let: Block scoped.
const: Block scoped.

 Ex:

 function demo(){
     var a =20;
     console.log(a); 

   if (true){

   var x = "var";
   let y = "let";
   const z = ""const;     /// block scop

   console.log(x);
   console.log(y);    // all working good ...if block
   console.log(z);

  }
   console.log(x); // outer block code run successfully  (var)   
   console.log(y);   // error  (let)
   console.log(z);   // error not defienfd  (const)

 demo();

console.log(a)