10/21

jQuery
Some cool tools around the web
JavaScript Libraries
Drawing libraries
HTML Frameworks
Conventions

You need to make sure your code works on all browsers.
Some very popular browsers don’t implement basic things according to a standard.
Therefore, you often need to have special cases for basic things like event handling.

People use JavaScript libraries to avoid needing to take care of all these special cases themselves.
Libraries handle different browser cases so you don’t have to.

One of the most popular JavaScript libraries.
If you don’t use it, you will at least need to deal with it.
What it does.
Allows you to easily select HTML elements
Allows you to manipulate these elements, define event handlers, do animation, and do AJAX calls more easily

Download the JavaScript library from http://jquery.com
Can also use hosted locations like Google Library API http://code.google.com/apis/libraries/
Also links you to some of the most popular JavaScript libraries.

1. Make it easy to run a function when your page loads.
2. Select a bunch of DOM elements and do something with them
3. Handle events
4. Do AJAX calls easily

There are 4 overloads total, I will only discuss 2 today.
jQuery(function (){…}): function passed in gets executed when the DOM loads.
Equivalent to calling document.ready(); which is when all the
DOM elements have loaded (but not necessarily all images).
similar to window.onload = function() {…} except window.onload waits for images to load too.

Pop up an alert saying “hello, world!” once the document loads.
$(document).ready(function() { alert("hello world");
});
OR
$(function(){ alert("hello, world!");
});
OR function helloWorld() { alert("hello world");
}
$(helloWorld);

jQuery has a focus on queries:
You do a query to get a list of objects back (jQuery objects).
You can then do interesting things with these objects.
jQuery defines one global function: jQuery()
So commonly used that jQuery defines a global symbol, $ for it.

jQuery() function (or, $() ) is ‘overloaded’
Remember when I said JavaScript doesn’t support overloading?
Well, you can write overloading yourself by checking your parameters.
Most basic parameter to $() : string representing a “css selector”
A “CSS Selector” is a string (query) which selects some subset of elements in your DOM.
For example, $("div") gets all divs,
$(".className") gets all elements whose class is className.

For loop that turns all h1 elements red var h1s = $("h1"); for (var i = 0; i < h1s.length; i++) { h1s[i].style.color="red";
}

css() allows you to either get the css properties of an element or set the css properties of an element.
Method is overloaded by checking for existence of variables.
Setting the text color of element with myId to red:
$("#myId").css({color: "red"});
If multiple elements returned, executes on all elements found .
Returns list of modified elements (chainable!)

Getting the text color of element with id “myId”:
$(“#myId”).css(“color”);
If multiple elements returned, executes on first element found.
Does not return a list (terminates your chain).
Setting the text color of element with id “myId” red:
$(“#myId”).css({color: “red”});

Add a CSS class to an element:
$("#myId").addClass("myClassName");
Toggle a CSS class:
If element has the class, remove it. If it doesn’t have the class, add it.
$("#myId").toggleClass("highlight");
More at http://api.jquery.com/category/css/

text() gets/sets the inner text of an element and its children.
html() gets/sets the inner HTML of an element and its children.
Example: Get the text of the first h1 element:
$(“h1”).text();
Example: Set the text of each h1 element to be “foobar”
$(“h1”).text(“foobar”);
Example: Add section numbers to each header element
$(“h1”).text(function(n, current){ return “section “ + (n+1) + “: “ + current
});

offset() gets/sets the position of an element relative to the entire document.
position() gets/sets the position of an element relative to its parent.
Example: scroll all elements with class “scrolling” left to right: function scrollText(){
$(".scrolling").offset(function(index, curpos){ return { left: (curpos.left + 5) % $(window).width(), top: (curpos.top)
};
}); setTimeout(scrollText, 30);
}

Allows you to associate data with any jQuery object (i.e. object that’s a result of a query).
Example: set some data for all div elements:
$("div").data("x",5);
Example: query data:
$("div").data("x") : get “x” property
$("div").data() : return object with all properties.

Methods that add/remove elements to your HTML document.
You can either pass in Element objects or HTML strings.
$("#myId").append(document.createElement("h r"));
Adds an <hr> element at end of element with id myId
$("#myId").after("<hr />")
Inserts an <hr> element directly after element with id myId.

Most jQuery methods operate on a list of objects, then return the modified list.
This allows you to chain methods, i.e. do multiple things on one line
Example:
Set text color of all h1 elements to green and add an hr element before and after these elements:

Most jQuery methods operate on a list of objects, then return the modified list.
This allows you to chain methods, i.e. do multiple things on one line
Example:
Set text color of all h1 elements to green and add an hr element before and after these elements:
$(“h1”).css({color: “green”}).before(“<hr />”).after(“<hr />”);

$(“h1”).css({color: “green”}).before(“<hr />”).after(“<hr />”);

$(“h1”).
css({color: “green”}).before(“<hr />”).after(“<hr />”);
<h1>
<h1>
<h1>

$(“h1”).
css({color: “green”}).
before(“<hr />”).after(“<hr />”);
<h1>
<h1>
<h1>
<h1>
<h1>
<h1>

$(“h1”).css({color: “green”}).
before(“<hr />”).
after(“<hr />”);
<h1>
<h1>
<h1>
<h1>
<h1>
<h1>
<hr/>
<h1>
<hr/>
<h1>
<hr/>
<h1>

$(“h1”).css({color: “green”}).before(“<hr />”).
after(“<hr />”);
<h1>
<h1>
<h1>
<h1>
<h1>
<h1>
<hr/>
<h1>
<hr/>
<h1>
<hr/>
<h1>
<hr/>
<h1>
<hr/>
<hr/>
<h1>
<hr/>
<hr/>
<h1>
<hr/>

Event handling is especially annoying because IE implements a different event API than other browsers.
Instead of addEventListener, uses attachEvent
Makes it a big pain to do event handling cross-browser.
jQuery makes it much easier for us to do event handling.

Example: clicking on <p> element toggles its background color.
Define class “highlighted” to have a grey background color.
$("p").on("click", function(){
$(this).toggleClass("highlighted");
})

jQuery does pass in parameters to the event handler
First argument is the event object, contains info about the event.
Stuff like target, clientX, etc.
For more information: http://api.jquery.com/category/events/event-object/
Return value of your event handler is important:
If it returns false the default action of event and any future propagation are canceled

scroll() click() change() dblclick() focus() hover() keypress() load()
Many more at http://api.jquery.com/category/events/

Useful debugging blurb that shows you the position of your mouse relative to the window.

jQuery has pretty powerful animation framework which allows you to smoothly change css properties of DOM elements.
Animations add polish to your site.
Examples of animations: http://api.jquery.com/fadeIn/

Every function has a duration that says how long the effect should last for.
Specify in ms or a string. “fast”, “slow”.
Animations are asynchronous.
Can specify a second parameter to your animation: the function to execute when your animation is complete.

fadeIn(speed, callback):
$("div").fadeIn(); fades in all divs.
$("div").fadeIn("fast"); fades in all divs fast.
fadeOut(speed, callback) fadeTo({fade options such as opacity to fade to}, speed, callback);

hide():
Animates width and height to 0 show():
Animates width and height from 0
Toggle()
Toggles between show and hide.

You can execute one animation after another by doing:
$("#myElement").fadeIn().fadeOut();

Use animate() to specify custom animation of css styles.
$("img").animate({height: 0}, {duration:
"fast", complete: function(){…})) quickly animates all images to have a height of 0 and executes a specified function on completion.
The first parameter specifies what properties you should animate to.
The second parameter (function object) is optional.

Some people find animations jarring.
jQuery.fx.off = true disables all jQuery animations.
To stop a current element from animating, you can use stop(). This stops the current element from animating.
You can also use delay(ms) to delay animations

Fading images on mouseover
$("img").mouseover(function(){
$(this).stop().fadeTo(300, 1.0);
};
$("img").mouseout(function(){
$(this).stop().fadeTo(300, 0.5);
}
Example taken from JavaScript: the definitive guide by David Flanagan

Fading images on mouseover
$("img").mouseover(function(){
$(this).stop().fadeTo(300, 1.0);
};
$("img").mouseout(function(){
$(this).stop().fadeTo(300, 0.5);
}
Example taken from JavaScript: the definitive guide by David Flanagan

getting or saving data from servers somewhere not getting into it in this class but check out $.ajax, $.get,
$.post if you're interested.

UnderscoreJS jQuery
PrototypeJS
MooTools

jQuery UI jQuery Mobile
Bootstrap
YUI

AngularJS
Backbone

Raphaël
ProcessingJS
PaperJS

http://acko.net/blog/this-is-your-brain-on-css/ http://www.nike.com/jumpman23/aj2012/ http://www.inception-explained.com/