{"id":148,"date":"2013-09-05T17:40:32","date_gmt":"2013-09-05T17:40:32","guid":{"rendered":"http:\/\/aurelio.audero.it\/blog\/?p=148"},"modified":"2022-08-16T23:04:52","modified_gmt":"2022-08-16T23:04:52","slug":"how-to-create-custom-filters-in-jquery","status":"publish","type":"post","link":"https:\/\/www.audero.it\/blog\/2013\/09\/05\/how-to-create-custom-filters-in-jquery\/","title":{"rendered":"How to Create Custom Filters in jQuery"},"content":{"rendered":"

In some cases you may need a shortcut to collect elements for which jQuery doesn’t provide a specific filter. This is exactly where custom filters come into play.<\/p>\n

In this article, extracted from my book Instant jQuery Selectors<\/a>, you’ll learn how to build a custom filter in jQuery<\/a>. Please note that, to be a complete post, it has some minor adjustment compared to the original recipe titled Custom filters (Become an expert)<\/cite>.
\n<\/p>\n

\"jquery<\/p>\n

\n\"Instant<\/a>
\nThis article is extracted from my book Instant jQuery Selectors<\/a>. Consider buying it on the Packt Publishing website<\/a> or on Amazon<\/a>.<\/p>\n

Instant jQuery Selectors<\/cite> is a practical guide that will teach you how to use jQuery’s selectors efficiently in order to easily select the elements of your pages to operate upon with jQuery’s methods. You will go through the most common problems that you could face while developing your project and will learn how to solve them with the help of focused examples that Instant jQuery Selectors<\/cite> has to offer.\n<\/div>\n

How to do it…<\/h2>\n

Our goal is to print the length of the elements having the placeholder attribute set, taking advantage of a previously created custom filter. In addition, to see all of the available options in action, we’ll create a second filter to collect all of the elements having a name with less than a given number of characters.<\/p>\n

To complete the task, follow the steps described below.<\/p>\n

Step 1<\/h3>\n

Create a file and rename it as custom-filters.html<\/code>.<\/p>\n

Step 2<\/h3>\n

Open the file using a simple text editor, like Notepad++ on Windows, Sublime on Mac, or Gedit on Linux, or with your favourite IDE. In this file, we’ll create a simple form with some typical fields like “Name”, “Surname”, and so on. All these fields have the specification of the type (type<\/code> attribute) and the name (name<\/code> attribute), but few of them also have a placeholder set (placeholder<\/code> attribute).<\/p>\n

Now, that you know what we’ll put in the file, just copy the HTML code below and save the changes.<\/p>\n

\r\n<!DOCTYPE html>\r\n<html>\r\n   <head>\r\n      <meta charset="UTF-8">\r\n      <title>Instant jQuery Selector How-to<\/title>\r\n      <style>\r\n         input,\r\n         select,\r\n         textarea\r\n         {\r\n            display: block;\r\n         }\r\n      <\/style>\r\n      <!-- Script will be placed here... -->\r\n   <\/head>\r\n   <body>\r\n      <form name="registration-form" id="registration-form" action="registration.php" method="post">\r\n         <label>Name:<\/label>\r\n         <input type="text" name="name" placeholder="Name" \/>\r\n         <label>Surname:<\/label>\r\n         <input type="text" name="surname" placeholder="Surname" \/>\r\n         <label>Email:<\/label>\r\n         <input type="email" name="email" placeholder="Email" \/>\r\n         <label>Phone:<\/label>\r\n         <input type="tel" name="phone-number" placeholder="Phone number" disabled="disabled" \/>\r\n         <label>Privacy:<\/label>\r\n         <input name="privacy" type="checkbox" checked="checked" \/>\r\n         <label>Contact me:<\/label>\r\n         <input name="contact-me" type="checkbox" \/>\r\n         <label>Sex:<\/label>\r\n         <select name="sex">\r\n            <option selected="selected" value="m">Male<\/option>\r\n            <option value="f">Female<\/option>\r\n         <\/select>\r\n         <input type="submit" value="Register" \/>\r\n      <\/form>\r\n   <\/body>\r\n<\/html>\r\n<\/pre>\n
Step 3<\/h3>\n
Replace the comment we put (<!-- Script will be placed here... --><\/code>) with the following code:<\/p>\n
\r\n<script src="http:\/\/ajax.googleapis.com\/ajax\/libs\/jquery\/1.10.1\/jquery.min.js"><\/script>\r\n<script>\r\n    $.expr[':'].placeholder = function(elem) {\r\n        return $(elem).attr('placeholder') !== undefined;\r\n    };\r\n    $.expr[':'].nameLengthLessThan = \r\n    $.expr.createPseudo(function(filterParam) {\r\n        var length = parseInt(filterParam);\r\n        return function(elem, context, isXml) {\r\n            return $(elem).attr('name') !== undefined && \r\n            $(elem).attr('name').length < length;\r\n      }\r\n    });\r\n    $(document).ready(function() {\r\n        console.log($(':placeholder').length);\r\n        console.log($('input:nameLengthLessThan(5)').length);\r\n    });\r\n<\/script>\r\n<\/pre>\n
Step 4<\/h3>\n
Save the file and open it with your favorite browser. Once the page is loaded, look at the console’s output.<\/p>\n
How it works…<\/h2>\n
At the very beginning of our JavaScript instructions for this page, we’ve added a property, or more specifically a function called placeholder to the :<\/code> (yes, it’s a property called colon, you read it right) attribute that belongs to the jQuery’s expr<\/code> attribute. :<\/code> is a property containing jQuery’s native filters and you can use it to add your own at runtime. Inside the function definition, we just have a single statement that checks if the current element has the placeholder attribute set, and if so, it returns true to keep the element.<\/p>\n
As you can see from the example, in this basic version, a filter is nothing but a function that accepts as an argument the current DOM element to process and needs to return true to keep it in the collection, and false to discard it. You should use this method when the following are true:<\/p>\n