jQuery Basics - Getting Started

So what is jQuery? From the jQuery web site: "jQuery is a fast and concise موجز JavaScript Library that simplifies HTML document traversing اجتياز, event handling, animating, and Ajax interactions for rapid تسريع web development. jQuery is designed to change the way that you write JavaScript." jQuery will help you write JavaScript faster using a simpler syntax. Instead of writing extra lines of code or the writing the same code over and over, you can use jQuery to consolidate تعزيز the code. jQuery will do the heavy lifting while you can concentrate on the more important stuff. jQuery also supports the idea of plugins. Plugins allow people to create mini-libraries that complement jQuery. The plugins can be anything from form validation to picture slide shows. We will look at plugins in future articles.

Where to Start

The first thing you will need to do to start using jQuery is to decide if you want to host the jQuery library or use a content delivery network (CDN). If you plan on hosting the jQuery library, you will need to download it from the jQuery web site (http://jquery.com) and upload it to your web server. The best way to use jQuery is to use a CDN. Both Microsoft and Google offer jQuery on their CDNs. There are several advantages to doing this. The first is that a CDN is spread out over the Internet. When someone comes to your web site and requests the jQuery library, it will be provided to them by the closestالاقرب hosting site. This will help speed up the download of the library to their local machine. Which brings us to another point, the jQuery library is cached on the user's machine to help with speed. The second reason is that if the user has been to another web site that had this CDN reference, the user will already have the jQuery file on their system. This will speed up the loading of your web page since they will not need to download the file again.When you are looking at the different libraries for jQuery, you will notice there are two. One of them has a ".min" in the file name. This is a "minified" version of the file. It is smaller and will load faster. Why two versions? The non-minified version is easier to read, but since there is a lot of white space, it makes the file larger. It is used to help with debugging. So whenever possible, always use the CDN and the minified version. This will help speed up your web site.Next we need to create a reference to the jQuery library. This is done by adding a line in between the opening (<head>) and closing (</head>) HTML header tags. We will use the Microsoft CDN.

<head>

</head>

jQuery works like normal JavaScript in the fact that you use <script> tags to denote the script. These can be placed in the head section or the body section of your web page.

Your script goes here

</script>

</script>

                       <script type="text/javascript">

                       </script>

               </head>

               <body>

                       <a href="#">Click Me</a>

               </body>

        </html>

Currently, the link "Click Me" does nothing. Let us change that. Enter the code below in between the script tags.

        $(document).ready(function(){

               $("a").click(function(event){

                       alert("You clicked me!");

});

});

What we did here was add a click event to the "Click Me" link. When it was clicked, it showed a JavaScript alert.

What is Up with the $

The dollar sign ($) denotes a jQuery constructor. It can be written either as $() or jQuery(). The dollar sign is just a shortcut. All jQuery constructors must start with this.The constructor starts with a $ and the selector is enclosed in parenthesis. A selector can be an element (tag), an element ID, an element class name. This is similar to the way CSS works. In the example above, we used the anchor tag (a) as a selector. When you use a selector, jQuery searches through the Document Object Model (DOM) to find all selectors that match. In the case of the example above, if we had more than one anchor tag, all anchor tags would now have a click event. Since selectors work similar to CSS, you will need to specify the selectors in a similar way. When referencing HTML elements, you will just use the element as is. See the following examples:

        $("a") - all anchor tags

        $("p") - all paragraph tags

        $("p.subject") - all paragraph tags with a class of subject

When referencing class names, you must specify the period (.) before the class name as in the following examples:

        $(".subject") - all elements with the class name of subject

        $("p.subject") - all paragraph tags with a class of subject

And last, when referencing IDs, you must specify the # before the ID name:

        $("#subject") - the element with the ID of subject

There are a few other types of selectors and we will talk about those in future articles. For now, these basic selectors should get you started.

Making Sure the Document is Ready

As with JavaScript, you may want to execute your jQuery code after the HTML document has completely loaded and is ready to be manipulated. This is where the $(document).ready function comes in to play. This will keep the JavaScript and jQuery code unloaded until the document is ready. Once the document has loaded, the function will execute. This keeps the code from executing before the document is ready which could cause issues. If you tried to manipulate a DOM element before it was ready, you would lose that functionality.

Conclusion

This article should be able to get you started using jQuery. The great thing about jQuery is that is does not replace JavaScript, just makes it better. Check back later as we will dive deeper into jQuery.

Adding jQuery to Your Web Pages

There are several ways to start using jQuery on your web site. You can:

Download the jQuery library from jQuery.com
Include jQuery from a CDN, like Google

Downloading jQuery

There are two versions of jQuery available for downloading:

Production version - this is for your live website because it has been minified and compressed
Development version - this is for testing and development (uncompressed and readable code)

Both versions can be downloaded from jQuery.com. The jQuery library is a single JavaScript file, and you reference it with the HTML <script> tag (notice that the <script> tag should be inside the <head> section):

Alternatives to Downloading

If you don't want to download and host jQuery yourself, you can include it from a CDN (Content Delivery Network). Both Google and Microsoft host jQuery. To use jQuery from Google or Microsoft, use one of the following:

Google CDN:

jQuery Syntax

The jQuery syntax is tailor made for selecting HTML elements and performing some action on the element(s).

Basic syntax is: $(selector).action()

A $ sign to define/access jQuery
A (selector) to "query (or find)" HTML elements
A jQuery action() to be performed on the element(s)

Examples:

$(this).hide() - hides the current element.

$("p").hide() - hides all <p> elements.

$(".test").hide() - hides all elements with class="test".

$("#test").hide() - hides the element with id="test".

The Document Ready Event

You might have noticed that all jQuery methods in our examples, are inside a document ready event:

$(document).ready(function(){

// jQuery methods go here...

});

This is to prevent any jQuery code from running before the document is finished loading (is ready). It is good practice to wait for the document to be fully loaded and ready before working with it. This also allows you to have your JavaScript code before the body of your document, in the head section. Here are some examples of actions that can fail if methods are run before the document is fully loaded: Trying to hide an element that is not created yet Trying to get the size of an image that is not loaded yet Tip: The jQuery team has also created an even shorter method for the document ready event:

$(function(){

// jQuery methods go here...

});

jQuery Selectors

jQuery selectors allow you to select and manipulate HTML element(s). jQuery selectors are used to "find" (or select) HTML elements based on their id, classes, types, attributes, values of attributes and much more. It's based on the existing CSS Selectors, and in addition, it has some own custom selectors. All selectors in jQuery start with the dollar sign and parentheses: $().

The element Selector

The jQuery element selector selects elements based on the element name. You can select all <p> elements on a page like this:

$("p")

Example

When a user clicks on a button, all <p> elements will be hidden:

<!DOCTYPE html>

$(document).ready(function(){

$("button").click(function(){

$("p").hide();

});

</script></head>

<body>

<h2>This is a heading</h2>

<p>This is a paragraph.</p>

<p>This is another paragraph.</p>

<button>Click me</button>

</body></html>

The #id Selector

The jQuery #id selector uses the id attribute of an HTML tag to find the specific element. An id should be unique within a page, so you should use the #id selector when you want to find a single, unique element. To find an element with a specific id, write a hash character, followed by the id of the element: $("#test")

Example: When a user clicks on a button, the element with id="test" will be hidden:

The .class Selector

The jQuery class selector finds elements with a specific class. To find elements with a specific class, write a period character, followed by the name of the class: $(".test")

Example: When a user clicks on a button, the elements with class="test" will be hidden:

Functions In a Separate File

If your website contains a lot of pages, and you want your jQuery functions to be easy to maintain, you can put your jQuery functions in a separate .js file. When we demonstrate jQuery in this tutorial, the functions are added directly into the <head> section. However, sometimes it is preferable to place them in a separate file, like this (use the src attribute to refer to the .js file):

Example

What are Events?

All the different visitor's actions that a web page can respond to are called events. An event represents the precise moment when something happens. Examples:

moving a mouse over an element
selecting a radio button
clicking on an element

The term "fires" is often used with events. Example: "The keypress event fires the moment you press a key".

Here are some common DOM events:

Mouse Events	Keyboard Events	Form Events	Document/Window Events
click	keypress	submit	load
dblclick	keydown	change	resize
mouseenter	keyup	focus	scroll
mouseleave		blur	unload

jQuery Syntax For Event Methods

In jQuery, most DOM events have an equivalent jQuery method. To assign a click event to all paragraphs on a page, you can do this: $("p").click(); The next step is to define what should happen when the event fires. You must pass a function to the event:

$("p").click(function(){
// action goes here!!
});

dblclick()

The dblclick() method attaches an event handler function to an HTML element. The function is executed when the user double-clicks on the HTML element: Example

$("p").dblclick(function(){
$(this).hide();
});

mouseenter()

The mouseenter() method attaches an event handler function to an HTML element. The function is executed when the mouse pointer enters the HTML element:

<!DOCTYPE html>

<head>

$(document).ready(function(){

$("#p1").mouseenter(function(){

alert("You entered p1!");

});

</script></head>

<body>

<p id="p1">Enter this paragraph.</p>

</body></html>

mouseleave()

The mouseleave() method attaches an event handler function to an HTML element.

The function is executed when the mouse pointer leaves the HTML element: Example

$("#p1").mouseleave(function(){
alert("Bye! You now leave p1!");
});

mousedown()

The mousedown() method attaches an event handler function to an HTML element. The function is executed, when the left mouse button is pressed down, while the mouse is over the HTML elemen

hover()

The hover() method takes two functions and is a combination of the mouseenter() and mouseleave() methods. The first function is executed when the mouse enters the HTML element, and the second function is executed when the mouse leaves the HTML element: Example

$("#p1").hover(function(){
alert("You entered p1!");
},
function(){
alert("Bye! You now leave p1!");
});

focus()

The focus() method attaches an event handler function to an HTML form field. The function is executed when the form field gets focus:

blur()

The blur() method attaches an event handler function to an HTML form field. The function is executed when the form field loses focus:

<!DOCTYPE html>

<head>

$(document).ready(function(){

$("input").focus(function(){

$(this).css("background-color","#cccccc");

});

$("input").blur(function(){

$(this).css("background-color","#ffffff");

});

</script></head>

<body>

Name: <input type="text" name="fullname"><br>

Email: <input type="text" name="email">

</body></html>

jQuery hide() and show()

With jQuery, you can hide and show HTML elements with the hide() and show() methods:

<!DOCTYPE html><head>

$(document).ready(function(){

$("#hide").click(function(){

$("p").hide();

});

$("#show").click(function(){

$("p").show();

});

</script></head>

<body>

<p>If you click on the "Hide" button, I will disappear.</p>

</body></html>

Syntax: $(selector).hide(speed,callback); $(selector).show(speed,callback);

The optional speed parameter specifies the speed of the hiding/showing, and can take the following values: "slow", "fast", or milliseconds. The optional callback parameter is a function to be executed after the hide() or show() method completes (you will learn more about callback functions in a later chapter). The following example demonstrates the speed parameter with hide():

<!DOCTYPE html>

<head>

$(document).ready(function(){

$("button").click(function(){

$("p").hide(1000);

});

</script></head>

<body>

<p>This is a paragraph with little content.</p> <p>This is another small paragraph.</p>

</body></html>

jQuery toggle()

With jQuery, you can toggle between the hide() and show() methods with the toggle() method. Shown elements are hidden and hidden elements are shown:

$("button").click(function(){
$("p").toggle();
});

$(selector).toggle(speed,callback);

jQuery Effects - Fading

With jQuery you can fade elements in and out of visibility.

<!DOCTYPE html>

$(document).ready(function(){

$("button").click(function(){

$("#div1").fadeIn();

$("#div2").fadeIn("slow");

$("#div3").fadeIn(3000);

});

</script></head>

<body>

<p>Demonstrate fadeIn() with different parameters.</p><button>Click to fade in boxes</button>

</body></html>

Effects - Sliding

<!DOCTYPE html>

$(document).ready(function(){

$("#flip").click(function(){

$("#panel").slideDown("slow");

});

</script>

#panel,#flip

{

padding:5px;

text-align:center;

background-color:#e5eecc;

border:solid 1px #c3c3c3;

}

#panel

{

padding:50px;

display:none;

}

jQuery Sliding Methods

With jQuery you can create a sliding effect on elements. jQuery has the following slide methods:

slideDown()
slideUp()
slideToggle()

The jQuery animate() method lets you create custom animations.

jQuery Animations - The animate() Method

The jQuery animate() method is used to create custom animations.

Syntax: $(selector).animate({params},speed,callback);

The required params parameter defines the CSS properties to be animated. The optional speed parameter specifies the duration of the effect. It can take the following values: "slow", "fast", or milliseconds. The optional callback parameter is a function to be executed after the animation completes. The following example demonstrates a simple use of the animate() method; it moves a <div> element to the left, until it has reached a left property of 250px:

<!DOCTYPE html><head>

$(document).ready(function(){

$("button").click(function(){

$("div").animate({left:'250px'});

});

</script> </head> <body><button>Start Animation</button>

<p>By default, all HTML elements have a static position, and cannot be moved. To manipulate the position, remember to first set the CSS position property of the element to relative, fixed, or absolute!</p>

</div></body></html>

jQuery animate() - Manipulate Multiple Properties

Notice that multiple properties can be animated at the same time:

Example

$("button").click(function(){
$("div").animate({
    left:'250px',
    opacity:'0.5',
    height:'150px',
    width:'150px'
});
});

jQuery animate() - Using Relative Values

It is also possible to define relative values (the value is then relative to the element's current value). This is done by putting += or -= in front of the value:

Example

$("button").click(function(){
$("div").animate({
    left:'250px',
    height:'+=150px',
    width:'+=150px'
});
});

jQuery animate() - Using Pre-defined Values

You can even specify a property's animation value as "show", "hide", or "toggle":

Example

$("button").click(function(){
$("div").animate({
height:'toggle'
});
});

jQuery animate() - Uses Queue Functionality

By default, jQuery comes with queue functionality for animations. This means that if you write multiple animate() calls after each other, jQuery creates an "internal" queue with these method calls. Then it runs the animate calls ONE by ONE. So, if you want to perform different animations after each other, we take advantage of the queue functionality:

<!DOCTYPE html><head>

$(document).ready(function(){

$("button").click(function(){

var div=$("div");

div.animate({height:'300px',opacity:'0.4'},"slow");

div.animate({width:'300px',opacity:'0.8'},"slow");

div.animate({height:'100px',opacity:'0.4'},"slow");

div.animate({width:'100px',opacity:'0.8'},"slow");

});

</script> </head><body><button>Start Animation</button>

The example below first moves the <div> element to the right, and then increases the font size of the text:

Example 2

<!DOCTYPE html>

$(document).ready(function(){

$("button").click(function(){

var div=$("div");

div.animate({left:'100px'},"slow");

div.animate({fontSize:'3em'},"slow");

});

</script> </head><body><button>Start Animation</button>

<div style="background:#98bf21;height:100px;width:200px;position:absolute;">HELLO</div></body></html>

The jQuery stop() method is used to stop animations or effects before it is finished.

jQuery stop() Method

The jQuery stop() method is used to stop an animation or effect before it is finished. The stop() method works for all jQuery effect functions, including sliding, fading and custom animations.

Syntax:

$(selector).stop(stopAll,goToEnd);

The optional stopAll parameter specifies whether also the animation queue should be cleared or not. Default is false, which means that only the active animation will be stopped, allowing any queued animations to be performed afterwards. The optional goToEnd parameter specifies whether or not to complete the current animation immediately. Default is false. So, by default, the stop() method kills the current animation being performed on the selected element. The following example demonstrates the stop() method, with no parameters:

<!DOCTYPE html><head>

$(document).ready(function(){

$("#flip").click(function(){

$("#panel").slideDown(5000);

});

$("#stop").click(function(){

$("#panel").stop();

});

</script> <style type="text/css">

#panel,#flip

{

padding:5px;

text-align:center;

background-color:#e5eecc;

border:solid 1px #c3c3c3;

}

#panel

{

padding:50px;

display:none;

}

</style></head><body> <button id="stop">Stop sliding</button><div id="flip">Click to slide down panel</div>

<div id="panel">Hello world!</div>

</body></html>

A callback function is executed after the current effect is 100% finished.

jQuery Callback Functions

JavaScript statements are executed line by line. However, with effects, the next line of code can be run even though the effect is not finished. This can create errors. To prevent this, you can create a callback function.

A callback function is executed after the current effect is finished.Typical syntax: $(selector).hide(speed,callback);

Examples

The example below has a callback parameter that is a function that will be executed after the hide effect is completed:

<!DOCTYPE html><head><script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script><script>

$(document).ready(function(){

$("button").click(function(){

$("p").hide("slow",function(){

alert("The paragraph is now hidden");

});

});</script></head><body><button>Hide</button><p>This is a paragraph with little content.</p></body></html>

<!DOCTYPE html><html><head><script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>

$(document).ready(function(){

$("button").click(function(){

$("p").hide("slow",function(){

alert("The paragraph is now hidden");

});

});</script></head><body><button>Hide</button><p>This is a paragraph with little content.</p></body></html>

The example below has no callback parameter, and the alert box will be displayed before the hide effect is completed:

<!DOCTYPE html>

$(document).ready(function(){

$("button").click(function(){

$("p").hide(1000);

alert("The paragraph is now hidden");

});

});</script></head><body><button>Hide</button><p>This is a paragraph with little content.</p></body></html>

With jQuery, you can chain together actions/methods. Chaining allows us to run multiple jQuery methods (on the same element) within a single statement.

jQuery Method Chaining

Until now we have been writing jQuery statements one at a time (one after the other). However, there is a technique called chaining, that allows us to run multiple jQuery commands, one after the other, on the same element(s). Tip: This way, browsers do not have to find the same element(s) more than once.To chain an action, you simply append the action to the previous action. The following example chains together the css(), slideUp(), and slideDown() methods. The "p1" element first changes to red, then it slides up, and then it slides down:

<!DOCTYPE html><html><head><script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>

$(document).ready(function()

{

$("button").click(function(){

$("#p1").css("color","red").slideUp(2000).slideDown(2000);

});

});</script></head><body><p id="p1">jQuery is fun!!</p><button>Click me</button></body></html>

We could also have added more method calls if needed. Tip: When chaining, the line of code could become quite long. However, jQuery is not very strict on the syntax; you can format it like you want, including line breaks and indentations. This also works just fine:

<!DOCTYPE html><html><head><script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>

$(document).ready(function()

{

$("button").click(function(){

$("#p1").css("color","red")

.slideUp(2000)

.slideDown(2000);

});

</script></head><body><p id="p1">jQuery is fun!!</p><button>Click me</button></body></html>

jQuery contains powerful methods for changing and manipulating HTML elements and attributes.

jQuery DOM Manipulation

One very important part of jQuery is the possibility to manipulate the DOM.

jQuery comes with a bunch of DOM related methods that make it easy to access and manipulate elements and attributes.DOM = Document Object Model
The DOM defines a standard for accessing HTML and XML documents: "The W3C Document Object Model (DOM) is a platform and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure, and style of a document."

Get Content - text(), html(), and val()

Three simple, but useful, jQuery methods for DOM manipulation are:

text() - Sets or returns the text content of selected elements
html() - Sets or returns the content of selected elements (including HTML markup)
val() - Sets or returns the value of form fields

The following example demonstrates how to get content with the jQuery text() and html() methods:

<!DOCTYPE html><head><script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script><script>

$(document).ready(function(){

$("#btn1").click(function(){

alert("Text: " + $("#test").text());

});

$("#btn2").click(function(){

alert("HTML: " + $("#test").html());

});

</script></head><body><p id="test">This is some <b>bold</b> text in a paragraph.</p>

</body></html>

The following example demonstrates how to get the value of an input field with the jQuery val() method:

<!DOCTYPE html>

<head>

$(document).ready(function(){

$("button").click(function(){

alert("Value: " + $("#test").val());

});

</script></head>

<body>

<button>Show Value</button></body></html>

Get Attributes - attr()

The jQuery attr() method is used to get attribute values.

<!DOCTYPE html>

<html>

<head>

</script>

$(document).ready(function(){

$("button").click(function(){

alert($("#w3s").attr("href"));

});

</script></head>

<body>

<p><a href="http://www.w3schools.com" id="w3s">W3Schools.com</a></p>

<button>Show href Value</button></body></html>

Set Content - text(), html(), and val()

We will use the same three methods from the previous page to set content:

text() - Sets or returns the text content of selected elements
html() - Sets or returns the content of selected elements (including HTML markup)
val() - Sets or returns the value of form fields

<!DOCTYPE html>

$(document).ready(function(){

$("#btn1").click(function(){

$("#test1").text("Hello world!");

});

$("#btn2").click(function(){

$("#test2").html("<b>Hello world!</b>");

});

$("#btn3").click(function(){

$("#test3").val("Dolly Duck");

});

</script></head>

<body>

<p id="test1">This is a paragraph.</p>

<p id="test2">This is another paragraph.</p>

<p>Input field: <input type="text" id="test3" value="Mickey Mouse"></p>

<button id="btn3">Set Value</button></body></html>

A Callback Function for text(), html(), and val()

All of the three jQuery methods above: text(), html(), and val(), also come with a callback function. The callback function has two parameters: the index of the current element in the list of elements selected and the original (old) value. You then return the string you wish to use as the new value from the function.

<!DOCTYPE html>

<html>

$(document).ready(function(){

$("#btn1").click(function(){

$("#test1").text(function(i,origText){

return "Old text: " + origText + " New text: Hello world! (index: " + i + ")";

});

$("#btn2").click(function(){

$("#test2").html(function(i,origText){

return "Old html: " + origText + " New html: Hello <b>world!</b> (index: " + i + ")";

});

</script></head>

Set Attributes - attr()

The jQuery attr() method is also used to set/change attribute values.

$("button").click(function(){
$("#w3s").attr("href","http://www.w3schools.com/jquery");
});

The attr() method also allows you to set multiple attributes at the same time.

The following example demonstrates how to set both the href and title attributes at the same time:

<!DOCTYPE html>

$(document).ready(function(){

$("button").click(function(){

$("#w3s").attr({

"href" : "http://www.w3schools.com/jquery",

"title" : "W3Schools jQuery Tutorial"

});

</script></head>

<body>

<p><a href="http://www.w3schools.com" id="w3s">W3Schools.com</a></p>

<button>Change href and title</button>

<p>Mouse over the link to see that the href attribute has changed and a title attribute is set.</p>

</body></html>

A Callback Function for attr()

The jQuery method attr(), also come with a callback function. The callback function has two parameters: the index of the current element in the list of elements selected and the original (old) attribute value. You then return the string you wish to use as the new attribute value from the function.

The following example demonstrates attr() with a callback function:

Example

$("button").click(function(){

$("#w3s").attr("href", function(i,origValue){

return origValue + "/jquery";

});

Pages

jQuery

Where to Start

What is Up with the $

Making Sure the Document is Ready

Conclusion

Adding jQuery to Your Web Pages

Downloading jQuery

Alternatives to Downloading

Google CDN:

jQuery Syntax

The Document Ready Event

jQuery Selectors

The element Selector

The #id Selector

The .class Selector

Functions In a Separate File

Example

What are Events?

jQuery Syntax For Event Methods

jQuery hide() and show()

jQuery toggle()

jQuery Effects - Fading

Effects - Sliding

jQuery Sliding Methods

jQuery Animations - The animate() Method

jQuery animate() - Manipulate Multiple Properties

Example

jQuery animate() - Using Relative Values

Example

jQuery animate() - Using Pre-defined Values

Example

jQuery animate() - Uses Queue Functionality

Example 2

jQuery stop() Method

jQuery Callback Functions

jQuery Method Chaining

jQuery DOM Manipulation

Get Content - text(), html(), and val()

Get Attributes - attr()

Set Content - text(), html(), and val()

A Callback Function for text(), html(), and val()

Set Attributes - attr()

A Callback Function for attr()

Example

No comments:

Post a Comment

Interesting Links