jQuery: Tips, tricks and hints for better development and Performance

jQueryTips, tricks and hints
for better development and performance

Jonas De Smet - @glamorous_be - BarcampGhent 2009

Jonas De Smet
- 23 years “old” developer
- Fan of PHP, jQuery and JSON
- Barcamp virgin

- Lives in Waregem
- Plays rugby with RC Curtrycke
- In love with Eline, the girl of
his life

Todays Schedule
✓ What is jQuery?
✓ 10 Usefull tips for better development
✓ 10 Performance tips
✓ Some Q’s & hopefully some A’s

What is jQuery?
- JavaScript Library
- Easy document traversing
- Easy event handling
- Rapid web development
- ...

“jQuery is designed to change the way that you write JavaScript”
(from jQuery.com)

What is jQuery?
var elems = document.getElementsByTagName(“p”);
for(var i=0;i<elems.length;i++){
if(elems[i].className == “example”){
elems[i].onclick = function(){
alert(“this example doesn’t rocks!”);
this.className += “ clicked”;
return false;
}
}

What is jQuery?
$(“p.example”).click(function(){
$(this).addClass(“clicked”);
alert(“this example rocks!”);
return false;
});

Usefull tips
for better development

Usefull tips - #1
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">

<head>

<title>Title of the page</title>

<meta http-equiv="content-type" content="text/html;charset=utf-8" />

<script type="text/javascript">document.documentElement.className = 'js';</script>

<link rel="stylesheet" href="/style.css" type="text/css" media="screen" />
</head>

Avoid ﬂashing content

Usefull tips - #2
function testFunction()
{
console.time(‘test this cool function’);
var testString = “”;
for(i=0; i<1000; i++)
{
testString += “item ” + i;
}
console.timeEnd(‘test this cool function’);
}

//time will be logged in milliseconds

Use Firebug’s console loggings facilities

Usefull tips - #3
<script type=”text/javascript” src=”http://www.google.com/jsapi”></script>
<script type=”text/javascript”>
google.load(“jquery”, “1.3.2”);
google.setOnLoadCallback(function() {
//init your javascript code
});
</script>

<script type=”text/javascript” src=”http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/
jquery.min.js”></script>

Load jQuery from Google Code

Usefull tips - #4
<div class=”expanded”> <div>
<p>Some lorem ipsum</p> <p>Some lorem ipsum</p>
<span class=”btn”>Close</span> <span class=”btn”>Close</span>
</div> </div>

$(“.btn”).click(function() { $(“.btn”).click(function() {
var parent = $(this).parent(); var parent = $(this).parent();
if ( parent.hasClass(“expanded”) ) { if ( parent.data(“expanded”) ) {
parent.removeClass(“expanded”); parent.data(“expanded”, false);
} }
else { else {
parent.addClass(“expanded”); parent.data(“expanded”, true);
} }
} }

Storing states in classes or even better in .data()

Usefull tips - #5
$.expr[“:”]:extlinks = function(element){
var link = $(element).attr(“href ”);
var reg = new RegExp('^(?:f|ht)tp(?:s)?://([^/]+)', 'im');
var link_host = (link.match(re) != null) ? link.match(re)[1].toString() : “”;
var host = window.location.host;
return (link_host != host);
}

$(“a:extlinks”).attr(“target”,”_blank”);

<h3>Some links</h3>
<a href=”http://example.com”>Example</a>
<a href=”/intern/folder/”>Example</a>

Write custom ﬁlter selectors

Usefull tips - #6
function uglyObject()
{
//some object stuff
}

var example = new uglyObject();

$(example).bind(‘addFancy’, function() {
// Custom event handling for when the event ‘addFrancy’ is triggered
});

$(example).trigger(‘addFancy’);

Bind custom events to custom objects

Usefull tips - #7
if ($(“div”).length){
//code here
}

if ($(“div”)[0]){
// code here
}

// Alternatively
$(“div”).get();

$(“div”).get(0);
$(“div”).get()[0];

Check if an element exists

Usefull tips - #8
// List bound events:
console.dir( $(“#elem”).data(“events”) );

// Log ALL handlers for ALL events:
$.each($(“#elem”).data(“events”), function(i, event)
{
jQuery.each(event, function(i, handler){
console.log( handler.toString() );
});
});

// source: http://james.padolsey.com

Use jQuery’s event storage

Usefull tips - #9
$(“a”).bind(“click.myNamespace”, function() {
// Some code for the click event with namespace “myNamespace”
});

// Unbind all events with namespace “myNamespace”
$(“a”).bind(“click.my2ndNamespace”, function(){
// Some code for the click event with namespace “my2ndNamespace”
});

// Unbind events with namespace “myNamespace”, not events with “my2ndNamespace”
$(“a”).unbind(“.myNamespace”);

$(“#example”).data(“nameValue.aNameSpace”, “teststring”);

Namespace your events and stored data

Usefull tips - #10
$(“p”).click(somefunction);

$(“p span”).click(somefunction);

$(“p a”).click(somefunction);

// You can do the above easily in one line
$(“p, p a, p span”).click(somefunction);

Try to group your queries

Performance tips - #1
var $specialdiv = $(“#specialdiv”);

$specialdiv.filter(function(){
return $(this).hasClass(“clicked”); // Must return a Boolean
});
$specialdiv.filter(“.clicked”);

var $specialdiv = $(“#specialdiv”);

// before
var $specialspan = $(“#specialdiv span.on”);
// much better
var $specialspan = $specialdiv.find(“span.on”);

Use .find() or .filter() instead of a new selector

1. Use id’s before tags
$(“#mydiv”).addClass(“test”);

2. Use tags before classes
$(“p”).addClass(“test”);

3. Use classes with a tag
$(“p.example”).addClass(“test”);

var items = $(“.coolDivs”, $(“#anotherDiv”) );

// or

var items = $(“#anotherDiv .coolDivs”);

// or even better

var items = $(“#anotherDiv div.coolDivs”);

//or

var items = $(“div.coolDivs”, $(“#anotherDiv”) );

Give selectors a context

var $bigInputs = $(“#exampleForm input.big”);
$bigInputs.bind(“click”, clickfunction);
$bigInputs.addClass(“finished”);

// You can define an object in the global scope and access it later

window.$myobject = { test: $(“#divWithId”) };
$myobject.test.addClass(“yes”);

// Cache added elements to access them later instead of using .live()

var $newDiv = $(“<div />”).appendTo(“#anotherDiv”);
$newDiv.bind(“click”, clickfunction);

Cache jQuery objects and use a $-prefix

var $myElement = $(“#element”);

$myElement.css(“border”, “1px solid orange”).addClass(“bordered”).fadeIn(“fast”);

// another example
$myElement.ﬁnd(“p”).addClass(“yellow”).end().ﬁnd(“span”).css(“border”,”1px”);

// Make you plugins chainable!
$.fn.myPlugin = function()
{
return $(this).addClass(“coolstuff ”);
};

Chaining FTW, especially for plugin-development

//Wrap everything in one element

var $list = $(“#mylist”); var $list = $(“#mylist”);
var str = “”; var wrapped = “<ul>”;

for (i=0; i < 100; i++) for (i=0; i < 100; i++)
{ {
str += “<li>item “ + i + ”</li>”; wrapped += “<li>item “ + i + ”</li>”;
} }

$list.html(str); wrapped += “</ul>”;

$list.replaceWith(wrapped);

Avoid DOM manipulation & keep it to a minimum

var $myList = $(“#navigation”);

$myList.click(function(evt){
$target = $(evt.target);
if($target.is(“li”) )
{
doSomethingWhenListItemIsClicked();
}
return false;
});

// more about jQuery events on http://docs.jquery.com/Events/jQuery.Event

Event delegation / bubbling

var arr = [ "one", "two", "three", "four", "ﬁve" ];

$.each(arr, function() {
$("#" + this).text("My id is " + this + ".");
});

var arr = [ "one", "two", "three", "four", "ﬁve" ];

for ( i=0; i < arr.length; i++ ) {
$("#" + i).text("My id is " + i + ".");
});

Use a for-loop instead of .each()

Use shorthand for $(document).ready()
$(function () {
// your code
});

Use $(window).load() when possible
$(window).load( function () {
// your code to be excuted when every HTML element is loaded
}

$(document).ready occurs during page render while objects are downloading
$(window).load() event occurs after all objects are called by the HTML


Pack and minify your custom scripts (in one)

http://javascriptcompressor.com
http://dean.edwards.name/packer

Thank you for listening!
Twitter @glamorous_be

Github http://github.com/glamorous
Slideshare http://www.slideshare.net/glamorous
LinkedIn http://be.linkedin.com/in/glamorous

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