One of the best features of javascript is that its event based and Asynchronous. This means the system will idle until something happens and then execute the desired event. This lets us do very powerful things like very async HTTP requests.

Callbacks are amazing when the code starts getting long and performance is key. Javascript callbacks help us organize our code in a clean way. Also sending functions as a parameter is another good feature of javascript that most languages dont allow.

Example of a callback:

function get_data(url,callback){
     $.getJSON(url,function(data){
           callback(data);
     });
}

get_data('http://example.com/data.json',function(data){
      // This will be called when the getJSON function is done and returns us the data
});

So this code basically calls a HTTP request to get the JSON data, when it returns, it will pass the JSON data back to the callback function.

This lets us build much more object oriented code, and allows us to use functions much more anonymously. For instance the get_data function can be used for any JSON get data call with different callbacks for each case.

You can also pass callbacks:

function get_data(url,callback){
     $.getJSON(url,function(data){
           callback(data);
     });
}

function login(user,pass,callback){
      var url = 'http://example.com/login?u='+user+'&p='+pass;
      get_data(url,callback);
}

login('demo','demo',function(data){
     // This will be executed when the get_data call is completed:
     console.log(data);
});

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qrpike