how to write callback function in 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: 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);
});
Example 4: what are callbacks
/*
tl;dr: Callbacks are a way to force one function to complete,
before running another. Used for asynchronus programming.
*/
// Consider this example:
names = ['Anthony', 'Betty', 'Camie']
function addName(name, callback){
setTimeout(function(){
names.append(name)
callback()
}, 200)
}
function getNames(){
setTimeout(function(){
console.log(names)
}, 100)
}
addName('Daniel', getNames)
/*
addName('Daniel', getNames) is saying:
'finish the function addName() BEFORE running the function getNames()'
> 'getNames()' here is the callback
Without the call back in this example, getNames would finish
before addName. (setTimeout is used to force one function to go slower)
Callbacks are given as arguments to other functions
*/
Example 5: javascript callback function
const message = function() {
console.log("This message is shown after 3 seconds");
}
setTimeout(message, 3000);
Example 6: callback functions javascript
function isOddNumber(number) {
return number % 2;
}Code language: JavaScript (javascript)