JAVASCRIPT

callback function

function greeting(name) {
  alert('Hello ' + name);
}

function processUserInput(callback) {
  var name = prompt('Please enter your name.');
  callback(name);
}

processUserInput(greeting);

what are callback functions

// A function which accepts another function as an argument
// (and will automatically invoke that function when it completes - note that there is no explicit call to callbackFunction)
funct printANumber(int number, funct callbackFunction) {
    printout("The number you provided is: " + number);
}

// a function which we will use in a driver function as a callback function
funct printFinishMessage() {
    printout("I have finished printing numbers.");
}

// Driver method
funct event() {
   printANumber(6, printFinishMessage);
}

callback function

//Callback functions - are functions that are called AFTER something happened

  const foo = (number, callbackFunction) => {
    //first 
    console.log(number)
    
    //second - runs AFTER console.log() happened
    callbackFunction()
  }
  

callback function

// Create calculator calling different operators with functions in javascript 

function pow(value0, value1) {
    return Math.pow(value0, value1);
}

function mod(value0, value1) {
    return value0 % value1;
}

function div(value0, value1) {
    return value0 / value1;
}

function mul(value0, value1) {
    return value0 * value1;
}

function add(value0, value1) {
    return value0 + value1;
}

function subtract(value0, value1) {
    return value0 - value1;
}

function calculator(value0, value1, operator) {
    return operator(value0, value1);
}

console.log(calculator(2,5,mod));

how to make callback function javascript

function startWith(message, callback){
	console.log("Clearly written messages is: " + message);
  
  	//check if the callback variable is a function..
  	if(typeof callback == "function"){
    	callback(); //execute function if function is truly a function.
    }
}
//finally execute function at the end 
startWith("This Messsage", function mySpecialCallback(){
	console.log("Message from callback function");
})

callback() function with example

const checkfile = (x,callback)=>{
    if(typeof x !== 'number')
    return callback('not a number'); //(err,{})
    
    callback(false,'yes it is');
}


checkfile(4,(err, data)=>{
    if(err)
    console.log(err);
    else 
    console.log(err);
})

callback function

const ironMan = withGloves(withBoots(withArmor(withHelmet(TonyStark))));

Callback Function

function greeting(name) {
  alert(`Hello, ${name}`);
}

function processUserInput(callback) {
  const name = prompt("Please enter your name.");
  callback(name);
}

processUserInput(greeting);

JavaScript CallBack Function

// function
function greet(name) {
    console.log('Hi' + ' ' + name);
}

greet('Peter'); // Hi Peter