how to make a callback function javascript code example

Example 1: javascript callback

/*
A callback function is a function passed into another function
as an argument, which is then invoked inside the outer function
to complete some kind of routine or action. 
*/
function greeting(name) {
  alert('Hello ' + name);
}

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

processUserInput(greeting);
// The above example is a synchronous callback, as it is executed immediately.

Example 2: callback function js

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

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

processUserInput(greeting);

Example 3: 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);
}

Example 4: javascript pass function as parameter

//passing a function as param and calling that function
function goToWork(myCallBackFunction) {
    //do some work here
    myCallBackFunction();
}

function refreshPage() {
    alert("I should be refreshing the page");
}

goToWork(refreshPage);

Example 5: callback function

function createQuote(quote, callback){ 
  var myQuote = "Like I always say, " + quote;
  callback(myQuote); // 2
}

function logQuote(quote){
  console.log(quote);
}

createQuote("eat your vegetables!", logQuote); // 1

// Result in console: 
// Like I always say, eat your vegetables!

Example 6: create callback function javascript

function add(a, b, callback) {
  if (callback && typeof(callback) === "function") {
    callback(a + b);
  }
}

add(5, 3, function(answer) {
  console.log(answer);
});