Editing Callback (computer programming) (section)

=== JavaScript ===

In the following [[JavaScript]] code, function <code>calculate</code> uses parameter <code>operate</code> as a blocking callback. <code>calculate</code> is called with <code>multiply</code> and then with <code>sum</code> which act as callback functions.

<syntaxhighlight lang="javascript">
function calculate(a, b, operate) {
    return operate(a, b);
}
function multiply(a, b) {
    return a * b;
}
function sum(a, b) {
    return a + b;
}
// outputs 20
alert(calculate(10, 2, multiply));
// outputs 12
alert(calculate(10, 2, sum));
</syntaxhighlight>

The collection method {{code|.each()}} of the [[jQuery]] [[JavaScript libraries|library]] uses the function passed to it as a blocking callback. It calls the callback for each item of the collection. For example:

<syntaxhighlight lang="javascript">
$("li").each(function(index) {
  console.log(index + ": " + $(this).text());
});
</syntaxhighlight>

Deferred callbacks are commonly used for handling events from the user, the client and timers. Examples can be found in {{code|addEventListener}}, [[Ajax (programming)|Ajax]] and <code>[[XMLHttpRequest]]</code>.
<ref>{{cite web |url=https://udn.realityripple.com/docs/Mozilla/Creating_JavaScript_callbacks_in_components#JavaScript_functions_as_callbacks |title=Creating JavaScript callbacks in components |department=Archive |website=UDN Web Docs |at=sec. JavaScript functions as callbacks |language=en |type=Documentation page |accessdate=2021-12-16 |url-status=live|archive-url=https://web.archive.org/web/20211216020616/https://udn.realityripple.com/docs/Mozilla/Creating_JavaScript_callbacks_in_components |archive-date=2021-12-16 }}</ref> 

In addition to using callbacks in JavaScript source code, C functions that take a function are supported via js-ctypes.<ref>{{cite web |url=https://developer.mozilla.org.cach3.com/en-US/docs/Mozilla/js-ctypes/Using_js-ctypes/Declaring_and_Using_Callbacks<!--This page is not properly rendered--> |title=Declaring and Using Callbacks |editor1-last=Holley |editor1-first=Bobby |editor2-last=Shepherd |editor2-first=Eric |department=Docs |website=[[Mozilla Developer Network]] |language=en |type=Documentation page |accessdate=2021-12-16 |url-status=live |archive-url=https://web.archive.org/web/20190117092921/https://developer.mozilla.org/en-US/docs/Mozilla/js-ctypes/Using_js-ctypes/Declaring_and_Using_Callbacks |archive-date=2019-01-17}}</ref>