what is 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: anonymous function javascript
// There are several definitions
// Non-anonymous, you name it
function hello() { /* code */ }
// Call as usual
hello()
// The myriad of anonymous functions
// This is actually anonymous
// It is simply stored in a variable
var hello = function() { /* code */ }
// It is called the same way
hello()
// You will usually find them as callbacks
setTimeout(function(){ /* code */ }, 1000)
// jQuery
$('.some-element').each(function(index){ /* code */ })
// Or a self firing-closue
(function(){ /* code */ })()
Example 4: 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 5: javascript callback
// Create a callback in the probs, in this case we call it 'callback'
function newCallback(callback) {
callback('This can be any value you want to return')
}
// Do something with callback (in this case, we console log it)
function actionAferCallback (callbackData) {
console.log(callbackData)
}
// Function that asks for a callback from the newCallback function, then parses the value to actionAferCallback
function requestCallback() {
newCallback(actionAferCallback)
}
Example 6: javascript callback function
const message = function() {
console.log("This message is shown after 3 seconds");
}
setTimeout(message, 3000);