Programming a callback function within a jQuery plugin

Question

I'm writing a jQuery plug-in so I can reuse this code in many places as it is a very well used piece of code, the code itself adds a new line to a table which has been cloned from a hidden row, it continues to perform a load of manipulations on the new row.

I'm currently referencing it like this:

$(".abc .grid").grid();

But I want to include a callback so each area the plug-in is called from can do something a bit more unique when the row has been added. I've used the jQuery AJAX plug-in before, so have used the success callback function, but cannot understand how the code works in the background. Here's what I want to achieve:

$(".abc .grid").grid({
    row_added: function() {
        // do something a bit more specific here
    }
});

Here's my plug-in code

(function($){           

    $.fn.extend({ 

        //pass the options variable to the function
        grid: function() {

            return this.each(function() {

                grid_table=$(this).find('.grid-table > tbody');
                grid_hidden_row=$(this).find('.grid-hidden-row');
                //console.debug(grid_hidden_row);
                $(this).find('.grid-add-row').click(function(event) {
                /* 
                 * clone row takes a hidden dummy row, clones it and appends a unique row 
                 * identifier to the id. Clone maintains our jQuery binds
                 */

                    // get the last id
                    last_row=$(grid_table).find('tr:last').attr('id');
                    if(last_row===undefined) {
                        new_row=1;
                    } else {
                        new_row=parseInt(last_row.replace('row',''),10)+1;
                    }

                    // append element to target, changes it's id and shows it
                    $(grid_table).append($(grid_hidden_row).clone(true).attr('id','row'+new_row).removeClass('grid-hidden-row').show());

                    // append unique row identifier on id and name attribute of seledct, input and a
                    $('#row'+new_row).find('select, input, a').each(function(id) {
                        $(this).appendAttr('id','_row'+new_row);
                        $(this).replaceAttr('name','_REPLACE_',new_row);
                    });

                    // disable all the readonly_if_lines options if this is the first row
                    if(new_row==1) {
                        $('.readonly_if_lines :not(:selected)').attr('disabled','disabled');
                    }
                });

                $(this).find('.grid-remove-row').click(function(event) {
                /* 
                 * Remove row does what it says on the tin, as well as a few other house 
                 * keeping bits and pieces
                 */

                    // remove the parent tr
                    $(this).parents('tr').remove();

                    // recalculate the order value5
                    //calcTotal('.net_value ','#gridform','#gridform_total');

                    // if we've removed the last row remove readonly locks
                    row_count=grid_table.find('tr').size();
                    console.info(row_count);
                    if(row_count===0) {
                        $('.readonly_if_lines :disabled').removeAttr('disabled');
                    }

                });

            });

        }

    });

})(jQuery);

I've done the usually searching on elgooG... but I seem to be getting a lot of noise with little result, any help would be greatly appreciated.

Thanks!

Ninette

Answer 1

Maybe something like this?

$.fn.extend({ 

    //pass the options variable to the function
    grid: function(callbacks) {

        // The following can be used so you don't need
        // to test for callback existence in the rest 
        // of the plugin
        var defaults = {
            before: function() {},
            after: function() {},
            row_added: function() {}                
        }
        callbacks = $.extend({},defaults,callbacks);

        // perform callback
        if (callbacks.before)
            callbacks.before();

        return this.each(function() {
            // do stuff
            if (callbacks.row_added)
                callbacks.row_added();
            // do more stuff
        }

        // perform callback
        if (callbacks.after)
            callbacks.after();
   }
});

Call it with something like this:

$("#grid").grid({
    before: function() {},
    after: function() {},
    row_added: function() {}
});                                                              

EDIT: I just added default callbacks so that you don't need to test for the existence of the callbacks. Personally, I like to just test for existence before calling them, but you might prefer this route.

Selfseeker

Cheers, this makes it very easy to understand :-), many thanks! – Ninette

@ILMV: sure, no problem. I just added some code to show you how to have default callbacks so that you don't need to test for callback existence before calling them. Depending on what you are doing, you may need to use the call or apply methods of calling the callback functions. Using them will allow you to change the value of this inside the callback. – Selfseeker

Answer 2

Yuo can read this post:

http://www.learningjquery.com/2009/03/making-a-jquery-plugin-truly-customizable

which contains a paragraph on providing callback capabilities...

var defaults = {

    onImageShow : function(){}, // we define an empty anonymous function
                                // so that we don't need to check its
                                // existence before calling it.
    // ... rest of settings ...
};

// Later on in the plugin:     
$nextButton.bind('click', showNextImage);

function showNextImage() {
    // DO stuff to show the image here...
    // ...
    // Here's the callback:
    settings.onImageShow.call(this);
}

Cambric