how will you explain callback functions in Javascript to a beginner?

Question

I am vary new to Javascript (just know the syntax) and I am learning AngularJs. Lots of time, I find a function as an argument to other function. Are those callbacks? And also, in what situation, writing functions like this is needed? Thanks.

You could take a look at this http://stackoverflow.com/questions/9596276/how-to-explain-callbacks-in-plain-english-how-are-they-different-from-calling-o — kubuntu, Sep 16 '13 at 10:13
Hey Rex. Thanks for the comment. My point was if we can directly calculate something and return it immediately, why to have other function inside a function (which, I guess, does the same task), and also a call to that inner function? — exAres, Sep 16 '13 at 10:40

Chamika Sandamal · Accepted Answer · 2013-09-16T11:31:12.860

2

Are those callbacks?

Yes. those are called callbacks.

in what situation, writing functions like this is needed

You need to use callback function when you need to execute something just after the function you called. most probably if you are writing any async code, and if you need to do something when async task is completed, you will definitely need callback functions.for a example, if you need to do call a function when ajax request is completed, you have to use callbacks.

Updated with example based on request.

function myFunction(callback) {
    var v1, v2;
    // do your stuff and fill the variables.

    // Call the callback with filed variables
    callback(v1, v2);
}

function callbackFunction(a, b) {
    alert(a + " - " + b);
}

myFunction(callbackFunction);

edited Sep 16 '13 at 11:31

answered Sep 16 '13 at 10:17

Chamika Sandamal

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Thanks Chamika, it was helpful. But an example would make things more clear for me. Thanks. – exAres Sep 16 '13 at 10:41
@user2745266, see updated answer for an example. – Chamika Sandamal Sep 16 '13 at 11:31
@user2745266, Hope you wil accept the answer once you are eligible to do it. – Chamika Sandamal Sep 16 '13 at 11:53

score 0 · Answer 2 · answered Sep 16 '13 at 10:19

0

you have a function like

function addNumbers(nr1, nr2){

  return nr1+nr2;

}

then every time you want to add for example 2+5 you just call addNumbers(2, 5) and it will return 7

the function addNumbers is a callback function

answered Sep 16 '13 at 10:19

y0ruba

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score -1 · Answer 3 · answered Sep 16 '13 at 10:16

Function is just like any other data assigned to a variable, it can be defined, deleted, copied.

They are helpul in cases like

They let you pass functions without the need to name them (which means there are less global variables)
You can delegate the responsibility of calling a function to another function (which means there is less code to write)
They can help with performance

how will you explain callback functions in Javascript to a beginner?

3 Answers3