callback.js

//synchronous piece of code
// function h(x,fn){
//     console.log(x*x)
//     fn()
//     //h ->higher order function
//     //fn->callback
// }
// h(10,function fn(){
//     console.log("done with the callback")
// })

//asynchronous piece of code
console.log("start")
setTimeout(function f(){
    console.log("timer done")//because it will be executed after 3 seconds and the code is not executing line by line so it is called an asychronous piece of code.
},3000)
console.log("end")
// native functions are the functions which are known to java script like loops variables.
//there are also runtime functions like setTimeout which are executed in rutime engine.they cannot hamper the processing of native functions.