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jQuery Tips and Tricks

Posted by: admin November 2, 2017 Leave a comment

Questions:

Syntax

Data Storage

Optimization

Miscellaneous

Answers:

Creating an HTML Element and keeping a reference

var newDiv = $("<div />");

newDiv.attr("id", "myNewDiv").appendTo("body");

/* Now whenever I want to append the new div I created, 
   I can just reference it from the "newDiv" variable */

Checking if an element exists

if ($("#someDiv").length)
{
    // It exists...
}

Writing your own selectors

$.extend($.expr[":"], {
    over100pixels: function (e)
    {
        return $(e).height() > 100;
    }
});

$(".box:over100pixels").click(function ()
{
    alert("The element you clicked is over 100 pixels height");
});

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jQuery’s data() method is useful and not well known. It allows you to bind data to DOM elements without modifying the DOM.

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Nesting Filters

You can nest filters (as nickf showed here).

.filter(":not(:has(.selected))")

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I’m really not a fan of the $(document).ready(fn) shortcut. Sure it cuts down on the code but it also cuts way down on the readability of the code. When you see $(document).ready(...), you know what you’re looking at. $(...) is used in far too many other ways to immediately make sense.

If you have multiple frameworks you can use jQuery.noConflict(); as you say, but you can also assign a different variable for it like this:

var $j = jQuery.noConflict();

$j("#myDiv").hide();

Very useful if you have several frameworks that can be boiled down to $x(...)-style calls.

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Ooooh, let’s not forget jQuery metadata! The data() function is great, but it has to be populated via jQuery calls.

Instead of breaking W3C compliance with custom element attributes such as:

<input 
  name="email" 
  validation="required" 
  validate="email" 
  minLength="7" 
  maxLength="30"/> 

Use metadata instead:

<input 
  name="email" 
  class="validation {validate: email, minLength: 2, maxLength: 50}" />

<script>
    jQuery('*[class=validation]').each(function () {
        var metadata = $(this).metadata();
        // etc.
    });
</script>

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Live Event Handlers

Set an event handler for any element that matches a selector, even if it gets added to the DOM after the initial page load:

$('button.someClass').live('click', someFunction);

This allows you to load content via ajax, or add them via javascript and have the event handlers get set up properly for those elements automatically.

Likewise, to stop the live event handling:

$('button.someClass').die('click', someFunction);

These live event handlers have a few limitations compared to regular events, but they work great for the majority of cases.

For more info see the jQuery Documentation.

UPDATE: live() and die() are deprecated in jQuery 1.7. See http://api.jquery.com/on/ and http://api.jquery.com/off/ for similar replacement functionality.

UPDATE2: live() has been long deprecated, even before jQuery 1.7. For versions jQuery 1.4.2+ before 1.7 use delegate() and undelegate(). The live() example ($('button.someClass').live('click', someFunction);) can be rewritten using delegate() like that: $(document).delegate('button.someClass', 'click', someFunction);.

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Replace anonymous functions with named functions. This really supercedes the jQuery context, but it comes into play more it seems like when using jQuery, due to its reliance on callback functions. The problems I have with inline anonymous functions, are that they are harder to debug (much easier to look at a callstack with distinctly-named functions, instead 6 levels of “anonymous”), and also the fact that multiple anonymous functions within the same jQuery-chain can become unwieldy to read and/or maintain. Additionally, anonymous functions are typically not re-used; on the other hand, declaring named functions encourages me to write code that is more likely to be re-used.

An illustration; instead of:

$('div').toggle(
    function(){
        // do something
    },
    function(){
        // do something else
    }
);

I prefer:

function onState(){
    // do something
}

function offState(){
    // do something else
}

$('div').toggle( offState, onState );

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Defining properties at element creation

In jQuery 1.4 you can use an object literal to define properties when you create an element:

var e = $("<a />", { href: "#", class: "a-class another-class", title: "..." });

… You can even add styles:

$("<a />", {
    ...
    css: {
        color: "#FF0000",
        display: "block"
    }
});

Here’s a link to the documentation.

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instead of using a different alias for the jQuery object (when using noConflict), I always write my jQuery code by wrapping it all in a closure. This can be done in the document.ready function:

var $ = someOtherFunction(); // from a different library

jQuery(function($) {
    if ($ instanceOf jQuery) {
        alert("$ is the jQuery object!");
    }
});

alternatively you can do it like this:

(function($) {
    $('...').etc()    // whatever jQuery code you want
})(jQuery);

I find this to be the most portable. I’ve been working on a site which uses both Prototype AND jQuery simultaneously and these techniques have avoided all conflicts.

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Check the Index

jQuery has .index but it is a pain to use, as you need the list of elements, and pass in the element you want the index of:

var index = e.g $('#ul>li').index( liDomObject );

The following is much easier:

If you want to know the index of an element within a set (e.g. list items) within a unordered list:

$("ul > li").click(function () {
    var index = $(this).prevAll().length;
});

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Shorthand for the ready-event

The explicit and verbose way:

$(document).ready(function ()
{
    // ...
});

The shorthand:

$(function ()
{
    // ...
});

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On the core jQuery function, specify the context parameter in addition to the selector parameter. Specifying the context parameter allows jQuery to start from a deeper branch in the DOM, rather than from the DOM root. Given a large enough DOM, specifying the context parameter should translate to performance gains.

Example: Finds all inputs of type radio within the first form in the document.

$("input:radio", document.forms[0]);

Reference: http://docs.jquery.com/Core/jQuery#expressioncontext

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Not really jQuery only but I made a nice little bridge for jQuery and MS AJAX:

Sys.UI.Control.prototype.j = function Sys$UI$Control$j(){
  return $('#' + this.get_id());
}

It’s really nice if you’re doing lots of ASP.NET AJAX, since jQuery is supported by MS now having a nice bridge means it’s really easy to do jQuery operations:

$get('#myControl').j().hide();

So the above example isn’t great, but if you’re writing ASP.NET AJAX server controls, makes it easy to have jQuery inside your client-side control implementation.

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Optimize performance of complex selectors

Query a subset of the DOM when using complex selectors drastically improves performance:

var subset = $("");

$("input[value^='']", subset);

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Speaking of Tips and Tricks and as well some tutorials. I found these series of tutorials (“jQuery for Absolute Beginners” Video Series) by Jeffery Way are VERY HELPFUL.

It targets those developers who are new to jQuery. He shows how to create many cool stuff with jQuery, like animation, Creating and Removing Elements and more…

I learned a lot from it. He shows how it’s easy to use jQuery.
Now I love it and i can read and understand any jQuery script even if it’s complex.

Here is one example I like “Resizing Text

1- jQuery…

<script language="javascript" type="text/javascript">
    $(function() {
        $('a').click(function() {
            var originalSize = $('p').css('font-size'); // get the font size 
            var number = parseFloat(originalSize, 10); // that method will chop off any integer from the specified variable "originalSize"
            var unitOfMeasure = originalSize.slice(-2);// store the unit of measure, Pixle or Inch

            $('p').css('font-size', number / 1.2 + unitOfMeasure);
            if(this.id == 'larger'){$('p').css('font-size', number * 1.2 + unitOfMeasure);}// figure out which element is triggered
         });        
     });
</script>

2- CSS Styling…

<style type="text/css" >
body{ margin-left:300px;text-align:center; width:700px; background-color:#666666;}
.box {width:500px; text-align:justify; padding:5px; font-family:verdana; font-size:11px; color:#0033FF; background-color:#FFFFCC;}
</style>

2- HTML…

<div class="box">
    <a href="#" id="larger">Larger</a> | 
    <a href="#" id="Smaller">Smaller</a>
    <p>
    In today’s video tutorial, I’ll show you how to resize text every time an associated anchor tag is clicked. We’ll be examining the “slice”, “parseFloat”, and “CSS” Javascript/jQuery methods. 
    </p>
</div>

Highly recommend these tutorials…

http://blog.themeforest.net/screencasts/jquery-for-absolute-beginners-video-series/

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Asynchronous each() function

If you have really complex documents where running the jquery each() function locks up the browser during the iteration, and/or Internet Explorer pops up the ‘do you want to continue running this script‘ message, this solution will save the day.

jQuery.forEach = function (in_array, in_pause_ms, in_callback)
{
    if (!in_array.length) return; // make sure array was sent

    var i = 0; // starting index

    bgEach(); // call the function

    function bgEach()
    {
        if (in_callback.call(in_array[i], i, in_array[i]) !== false)
        {
            i++; // move to next item

            if (i < in_array.length) setTimeout(bgEach, in_pause_ms);
        }
    }

    return in_array; // returns array
};


jQuery.fn.forEach = function (in_callback, in_optional_pause_ms)
{
    if (!in_optional_pause_ms) in_optional_pause_ms = 10; // default

    return jQuery.forEach(this, in_optional_pause_ms, in_callback); // run it
};

The first way you can use it is just like each():

$('your_selector').forEach( function() {} );

An optional 2nd parameter lets you specify the speed/delay in between iterations which may be useful for animations (the following example will wait 1 second in between iterations):

$('your_selector').forEach( function() {}, 1000 );

Remember that since this works asynchronously, you can’t rely on the iterations to be complete before the next line of code, for example:

$('your_selector').forEach( function() {}, 500 );
// next lines of code will run before above code is complete

I wrote this for an internal project, and while I am sure it can be improved, it worked for what we needed, so hope some of you find it useful. Thanks –

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Syntactic shorthand-sugar-thing–Cache an object collection and execute commands on one line:

Instead of:

var jQueryCollection = $("");

jQueryCollection.command().command();

I do:

var jQueryCollection = $("").command().command();

A somewhat “real” use case could be something along these lines:

var cache = $("#container div.usehovereffect").mouseover(function ()
{
    cache.removeClass("hover").filter(this).addClass("hover");
});

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I like declare a $this variable at the beginning of anonymous functions, so I know I can reference a jQueried this.

Like so:

$('a').each(function() {
    var $this = $(this);

    // Other code
});

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Save jQuery Objects in Variables for Reuse

Saving a jQuery object to a variable lets you reuse it without having to search back through the DOM to find it.

(As @Louis suggested, I now use $ to indicate that a variable holds a jQuery object.)

// Bad: searching the DOM multiple times for the same elements
$('div.foo').each...
$('div.foo').each...

// Better: saving that search for re-use
var $foos = $('div.foo');
$foos.each...
$foos.each...

As a more complex example, say you’ve got a list of foods in a store, and you want to show only the ones that match a user’s criteria. You have a form with checkboxes, each one containing a criteria. The checkboxes have names like organic and lowfat, and the products have corresponding classes – .organic, etc.

var $allFoods, $matchingFoods;
$allFoods = $('div.food');

Now you can keep working with that jQuery object. Every time a checkbox is clicked (to check or uncheck), start from the master list of foods and filter down based on the checked boxes:

// Whenever a checkbox in the form is clicked (to check or uncheck)...
$someForm.find('input:checkbox').click(function(){

  // Start out assuming all foods should be showing
  // (in case a checkbox was just unchecked)
  var $matchingFoods = $allFoods;

  // Go through all the checked boxes and keep only the foods with
  // a matching class 
  this.closest('form').find("input:checked").each(function() {  
     $matchingFoods = $matchingFoods.filter("." + $(this).attr("name")); 
  });

  // Hide any foods that don't match the criteria
  $allFoods.not($matchingFoods).hide();
});

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It seems that most of the interesting and important tips have been already mentioned, so this one is just a little addition.

The little tip is the jQuery.each(object, callback) function. Everybody is probably using the jQuery.each(callback) function to iterate over the jQuery object itself because it is natural. The jQuery.each(object, callback) utility function iterates over objects and arrays. For a long time, I somehow did not see what it could be for apart from a different syntax (I don’t mind writing all fashioned loops), and I’m a bit ashamed that I realized its main strength only recently.

The thing is that since the body of the loop in jQuery.each(object, callback) is a function, you get a new scope every time in the loop which is especially convenient when you create closures in the loop.

In other words, a typical common mistake is to do something like:

var functions = [];
var someArray = [1, 2, 3];
for (var i = 0; i < someArray.length; i++) {
    functions.push(function() { alert(someArray[i]) });
}

Now, when you invoke the functions in the functions array, you will get three times alert with the content undefined which is most likely not what you wanted. The problem is that there is just one variable i, and all three closures refer to it. When the loop finishes, the final value of i is 3, and someArrary[3] is undefined. You could work around it by calling another function which would create the closure for you. Or you use the jQuery utility which it will basically do it for you:

var functions = [];
var someArray = [1, 2, 3];
$.each(someArray, function(item) {
    functions.push(function() { alert(item) });
});

Now, when you invoke the functions you get three alerts with the content 1, 2 and 3 as expected.

In general, it is nothing you could not do yourself, but it’s nice to have.

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Access jQuery functions as you would an array

Add/remove a class based on a boolean…

function changeState(b)
{
    $("selector")[b ? "addClass" : "removeClass"]("name of the class");
}

Is the shorter version of…

function changeState(b)
{
    if (b)
    {
        $("selector").addClass("name of the class");
    }
    else
    {
        $("selector").removeClass("name of the class");
    }
}

Not that many use-cases for this. Never the less; I think it’s neat 🙂

Update

Just in case you are not the comment-reading-type, ThiefMaster points out that the toggleClass accepts a boolean value, which determines if a class should be added or removed. So as far as my example code above goes, this would be the best approach…

$('selector').toggleClass('name_of_the_class', true/false);

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Update:

Just include this script on the site and you’ll get a Firebug console that pops up for debugging in any browser. Not quite as full featured but it’s still pretty helpful! Remember to remove it when you are done.

<script type='text/javascript' src='http://getfirebug.com/releases/lite/1.2/firebug-lite-compressed.js'></script>

Check out this link:

From CSS Tricks

Update:
I found something new; its the the JQuery Hotbox.

JQuery Hotbox

Google hosts several JavaScript libraries on Google Code. Loading it from there saves bandwidth and it loads quick cos it has already been cached.

<script src="http://www.google.com/jsapi"></script>  
<script type="text/javascript">  

    // Load jQuery  
    google.load("jquery", "1.2.6");  

    google.setOnLoadCallback(function() {  
        // Your code goes here.  
    });  

</script>

Or

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.2.6/jquery.min.js" type="text/javascript"></script>

You can also use this to tell when an image is fully loaded.

$('#myImage').attr('src', 'image.jpg').load(function() {  
    alert('Image Loaded');  
});

The “console.info” of firebug, which you can use to dump messages and variables to the screen without having to use alert boxes. “console.time” allows you to easily set up a timer to wrap a bunch of code and see how long it takes.

console.time('create list');

for (i = 0; i < 1000; i++) {
    var myList = $('.myList');
    myList.append('This is list item ' + i);
}

console.timeEnd('create list');

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Use filtering methods over pseudo selectors when possible so jQuery can use querySelectorAll (which is much faster than sizzle). Consider this selector:

$('.class:first')

The same selection can be made using:

$('.class').eq(0)

Which is must faster because the initial selection of ‘.class’ is QSA compatible

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Remove elements from a collection and preserve chainability

Consider the following:

<ul>
    <li>One</li>
    <li>Two</li>
    <li>Three</li>
    <li>Four</li>
    <li>Five</li>
</ul>

$("li").filter(function()
{
    var text = $(this).text();

    // return true: keep current element in the collection
    if (text === "One" || text === "Two") return true;

    // return false: remove current element from the collection
    return false;
}).each(function ()
{
    // this will alert: "One" and "Two"       
    alert($(this).text());
});

The filter() function removes elements from the jQuery object. In this case: All li-elements not containing the text “One” or “Two” will be removed.

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Changing the type of an input element

I ran into this issue when I was trying to change the type of an input element already attached to the DOM. You have to clone the existing element, insert it before the old element, and then delete the old element. Otherwise it doesn’t work:

var oldButton = jQuery("#Submit");
var newButton = oldButton.clone();

newButton.attr("type", "button");
newButton.attr("id", "newSubmit");
newButton.insertBefore(oldButton);
oldButton.remove();
newButton.attr("id", "Submit");

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Judicious use of third-party jQuery scripts, such as form field validation or url parsing. It’s worth seeing what’s about so you’ll know when you next encounter a JavaScript requirement.

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Line-breaks and chainability

When chaining multiple calls on collections…

$("a").hide().addClass().fadeIn().hide();

You can increase readability with linebreaks. Like this:

$("a")
.hide()
.addClass()
.fadeIn()
.hide();

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Use .stop(true,true) when triggering an animation prevents it from repeating the animation. This is especially helpful for rollover animations.

$("#someElement").hover(function(){
    $("div.desc", this).stop(true,true).fadeIn();
},function(){
    $("div.desc", this).fadeOut();
});

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Using self-executing anonymous functions in a method call such as .append() to iterate through something. I.E.:

$("<ul>").append((function ()
{
    var data = ["0", "1", "2", "3", "4", "5", "6"],
        output = $("<div>"),
        x = -1,
        y = data.length;

    while (++x < y) output.append("<li>" + info[x] + "</li>");

    return output.children();
}()));

I use this to iterate through things that would be large and uncomfortable to break out of my chaining to build.

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HTML5 data attributes support, on steroids!

The data function has been mentioned before. With it, you are able to associate data with DOM elements.

Recently the jQuery team has added support for HTML5 custom data-* attributes. And as if that wasn’t enough; they’ve force-fed the data function with steroids, which means that you are able to store complex objects in the form of JSON, directly in your markup.

The HTML:

<p data-xyz = '{"str": "hi there", "int": 2, "obj": { "arr": [1, 2, 3] } }' />

The JavaScript:

var data = $("p").data("xyz");

data.str // "hi there"
typeof data.str // "string"

data.int + 2 // 4
typeof data.int // "number"

data.obj.arr.join(" + ") + " = 6" // "1 + 2 + 3 = 6"
typeof data.obj.arr // "object" ... Gobbles! Errrghh!