in1.js

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

 const sum = add(5, 90);
 console.log(sum)

 // arrow function

 const add3 = (a, b) => a + b

 sum3 = add3(90, 50);
 console.log(sum3);

 const diff = (x, y) => x - y;  // duble paramiture
 const multi = (first, secound, third) => first * secound * third; // multiple peramtr

 const double = num => num * 2;  //single paramtr

 // no parameter

 const getPI = () => Math.PI