notes.txt

//functions
//types of functions
//var,let and const
//hoisting
//block and scope
//template literals
//spread opertaor
//rest parameter
-------------------------------
1.functions:Set of statements that performs specific task
syntax: function functionname(parameter){ 
    //set of statements that perform specific task
   }
functionname(); //function call
example:
function mul(a,b){
    console.log(a*b)
}
mul(1,2);
//functions always have return
//Return: To reduce the number of times code executed.
//example:
function mul(a,b,c){
   return a*b*c
}
console.log(mul(1,2,3));
//functionname is userdefined
//if print without return then it shows undefined
//function is used for DRY codes.
//one function will have only one return keyword.
//print the odd numbers in an array
var arr = [12,13,14,15,16];
var result =[];
//function is used to extract the values(odd number)
function odd(arr){
    for(var i=0;i<arr.length;i++){
        if(arr[i]%2!=0){
           result.push(arr[i]);
        }
    }
    return result;
}
console.log(odd(arr));
--------------------------------
Types of function:
1.anonyomus function
2.IIFE(Immediately Invoked Function expression)
3.arrow function = ES6

-----------------
1.anonyomus function : a function without name.
function(){
    //set of statements
}()
example:
var arr = [12,13,14,15,17,19,21]
var result =[];
var odd = function(arr){
     for(var i=0;i<arr.length;i++){
        if(arr[i]%2!=0){
           result.push(arr[i]);
        }
    }
    return result;
}

console.log(odd(arr));
---------------------------------------------------
2.IIFE:
(function)(functioncall)

example
( function odd(arr){
  var result =[];
        for(var i=0;i<arr.length;i++){
            if(arr[i]%2!=0){
               result.push(arr[i]);
            }
        }
      console.log (result);
    }
   )([12,13,14,15,17,19,21])
   -------------------------------------------------------
3.Arrow functions: introduced in ES6
it has a => keyword and return keyword is must.
function a(){

}
this has been overcomed as
var a = (arr)=>{

}
example:
var odd = (arr)=>{
    var result =[];
        for(var i=0;i<arr.length;i++){
            if(arr[i]%2!=0){
               result.push(arr[i]);
            }
        }
        return result;
}
console.log(odd([12,13,14,15,17,19,21]))
---------------------------------------------
//function without parameter
function greet(){
    console.log("welcome");
}
greet();
-----------------------------------------------
//template literals
template literals help us to overcome concatenation
`${expression}`
//spread operator : converts a string into character array
//synatx: ...
//example1
var arr=["guvi"]
console.log(...arr);
//example 2: 
var arr1=["bob","join","sofia"]
var arr2 = ["rupan" , "guvi"]
var arr3 = [...arr2 , ...arr1];
console.log(arr3)
//rest parameter : it is used inside the function
//to consider remaining values
function foo(a,b,...rest){
    var sum =0;
    for(var i=0;i<rest.length;i++){
     sum = sum+rest[i];
    }
    return sum;
}
console.log(foo(12,13,14,15,16,17))
//a=12
//b=13