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Saturday, January 31, 2015
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Implementing Callback Functions in JQuery

11:50 PMSaturday, January 31, 2015
Callback function reference will execute after the current effect/function/event finished completely. This type of function can be used after any event completion like to set an element’s value after execution of some function finished.

In earlier article we have discussed about callback function execution after finishing effect. These functions executes after current effect have been finished. As the effect completed, the function reference specified as callback will be executed.

Following code block will change the text field of element having id "testComment" as mentioned in the code. This whole process will take place after button (btnComment) click event done.

$("#btnChange").click(function(){
  $("#testComment").text(function(i,origText){
    return "Old text: " + origText + " New text: Changed! on index: " + i;
  });
});

A callback function is one which is passed as an argument in another function and which is invoked after some kind of event. The call back nature of the argument is that, once its parent method completes, the function which this argument represents is then called; that is to say that the parent method calls back and executes the method provided as an argument.

So we can perform anything after any event or any ajax request also e.g. we want to change the html of a div element after clicking on a button, the following code fragment helps us:

$("#btnChange").click(function(){
  $("#testDiv").html(function(i,origText){
    return "Old html: " + origText + " New html: This is new HTML for this div element";
  });
});

Callbacks are so-called due to their usage with pointer languages. If you don't use one of those, just understand that it is just a name to describe a method that's supplied as an argument to other method, such that when the first method is called and its method body completes, the callback method is then invoked, or in other words "called at the back" of the other function.

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