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callback function?! what is it?!?

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  callback function?! what is it?!? Andrea <andrea.lorizzo@gmail.com> - 2014-08-21 07:22 -0700
    Re: callback function?! what is it?!? Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2014-08-21 18:39 -0300

#25717 — callback function?! what is it?!?

Hallo!
In line 121 at code in 
https://github.com/brianreavis/selectize.js/blob/master/examples/cities.html

there is a function called "calback"
I can not see where it is defined. What is it? is it a javascript function?
is it a Jquery function?
what does it do?

Thank you in advance for te time you'll spend for answering me
Andrea

P.S. following there is part of the code:

$select_state = $('#select-state').selectize({
  onChange: function(value) {
    if (!value.length) return;
    select_city.disable();
    select_city.clearOptions();
    select_city.load(function(callback) {
       xhr && xhr.abort();
       xhr = $.ajax({
       url: 'http://www.....te_of/' + value + '.json',
       success: function(results) {
                   select_city.enable();
                   callback(results);
                 },
       error: function() {
                   callback();
              }
    })
   });
}
});

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#25721

On 21/08/2014 11:22, Andrea wrote:
> Hallo!
> In line 121 at code in 
> https://github.com/brianreavis/selectize.js/blob/master/examples/cities.html
> 
> there is a function called "calback"
> I can not see where it is defined. What is it? is it a javascript function?
> is it a Jquery function?
> what does it do?
> 
> Thank you in advance for te time you'll spend for answering me
> Andrea
> 
> P.S. following there is part of the code:
> 
> $select_state = $('#select-state').selectize({
>   onChange: function(value) {
>     if (!value.length) return;
>     select_city.disable();
>     select_city.clearOptions();
>     select_city.load(function(callback) {
>        xhr && xhr.abort();
>        xhr = $.ajax({
>        url: 'http://www.....te_of/' + value + '.json',
>        success: function(results) {
>                    select_city.enable();
>                    callback(results);
>                  },
>        error: function() {
>                    callback();
>               }
>     })
>    });
> }
> });
> 

A callback function, or simply a "callback", is a function passed as a
parameter to other functions, in order to execute specific tasks and /
or after certain I/O operations

E.g.

function doSomething(callback) {
  var results;
  // compute some results
  if (typeof callback == "function") {
    callback(results);
  }
}

function write2Server(file) {
  // this will be called back in doSomething().
}

doSomething(write2Server);

-- 
Joao Rodrigues

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