Tuesday 9 April 2013

jQuery Tutorial

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What is jQuery?

jQuery is a lightweight, "write less, do more", JavaScript library.
The purpose of jQuery is to make it much easier to use JavaScript on your website.
jQuery takes a lot of common tasks that require many lines of JavaScript code to accomplish, and wraps them into methods that you can call with a single line of code.
jQuery also simplifies a lot of the complicated things from JavaScript, like AJAX calls and DOM manipulation.
The jQuery library contains the following features:
  • HTML/DOM manipulation
  • CSS manipulation
  • HTML event methods
  • Effects and animations
  • AJAX
  • Utilities

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...

});
Use the syntax you prefer. We think that the document ready event is easier to understand when reading the code.

jQuery Selectors

jQuery selectors allow you to select and manipulate HTML element(s).
With jQuery selectors you can find 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 type of selectors in jQuery, start with the dollar sign and parentheses: $().


The element Selector

Example:

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(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>

Example 2: The #Id Selector

 <!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("#test").hide();
  });
});
</script>
</head>

<body>
<h2>This is a heading</h2>
<p>This is a paragraph.</p>
<p id="test">This is another paragraph.</p>
<button>Click me</button>
</body>

</html>

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!!
});

Commonly Used jQuery Event Methods

$(document).ready()
The $(document).ready() method allows us to execute a function when the document is fully loaded. This event is already explained in the jQuery Syntax chapter.
click()
The click() method attaches an event handler function to an HTML element.
The function is executed when the user clicks on the HTML element.
The following example says: When a click event fires on a <p> element; hide the current <p> element:

Example

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


dblclick()
The dbclick() 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:

Example

$("#p1").mouseenter(function(){
  alert("You entered p1!");
});


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 element:

Example

$("#p1").mousedown(function(){
  alert("Mouse down over p1!");
});


mouseup()
The mouseup() method attaches an event handler function to an HTML element.
The function is executed, when the left mouse button is released, while the mouse is over the HTML element:

Example

$("#p1").mouseup(function(){
  alert("Mouse up over p1!");
});


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:

Example

$("input").focus(function(){
  $(this).css("background-color","#cccccc");
});


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

Example

$("input").blur(function(){
  $(this).css("background-color","#ffffff");
});

jQuery - Get Content and Attributes

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>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/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>
<button id="btn1">Show Text</button>
<button id="btn2">Show HTML</button>
</body>
</html> The following example demonstrates how to get the value of an input field with the jQuery val() method:

  <!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    alert("Value: " + $("#test").val());
  });
});
</script>
</head>

<body>
<p>Name: <input type="text" id="test" value="Mickey Mouse"></p>
<button>Show Value</button>
</body>
</html>

Get Attributes - attr()

The jQuery attr() method is used to get attribute values.
The following example demonstrates how to get the value of the href attribute in a link:

 <!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<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()

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(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="btn1">Set Text</button>
<button id="btn2">Set HTML</button>
<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.
The following example demonstrates text() and html() with a callback function:

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(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>

<body>
<p id="test1">This is a <b>bold</b> paragraph.</p>
<p id="test2">This is another <b>bold</b> paragraph.</p>
<button id="btn1">Show Old/New Text</button>
<button id="btn2">Show Old/New HTML</button>
</body>
</html>

Set Attributes - attr()

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("#w3s").attr("href","http://www.w3schools.com/jquery");
  });
});
</script>
</head>

<body>
<p><a href="http://www.w3schools.com" id="w3s">W3Schools.com</a></p>
<button>Change href Value</button>
<p>Mouse over the link (or click on it) to see that the value of the href attribute has changed.</p>
</body>
</html>

Add New HTML content

We will look at four jQuery methods that are used to add new content:
  • append() - Inserts content at the end of the selected elements
  • prepend() - Inserts content at the beginning of the selected elements
  • after() - Inserts content after the selected elements
  • before() - Inserts content before the selected elements

jQuery append() Method

The jQuery append() method inserts content AT THE END of the selected HTML elements.

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("#btn1").click(function(){
    $("p").append(" <b>Appended text</b>.");
  });

  $("#btn2").click(function(){
    $("#list").append("<li>Appended item</li>");
  });
});
</script>
</head>

<body>
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
<ol id="list">
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
</ol>
<button id="btn1">Append text</button>
<button id="btn2">Append list items</button>
</body>
</html>

jQuery prepend() Method

The jQuery prepend() method inserts content AT THE BEGINNING of the selected HTML elements.

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("#btn1").click(function(){
    $("p").prepend("<b>Prepended text</b>. ");
  });
  $("#btn2").click(function(){
    $("ol").prepend("<li>Prepended item</li>");
  });
});
</script>
</head>
<body>

<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
<ol>
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
</ol>

<button id="btn1">Prepend text</button>
<button id="btn2">Prepend list item</button>

</body>
</html>

jQuery after() and before() Methods

The jQuery after() method inserts content AFTER the selected HTML elements.
The jQuery before() method inserts content BEFORE the selected HTML elements.

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("#btn1").click(function(){
    $("img").before("<b>Before</b>");
  });

  $("#btn2").click(function(){
    $("img").after("<i>After</i>");
  });
});
</script>
</head>

<body>
<img src="/images/w3jquery.gif" alt="jQuery" width="100" height="140">
<br><br>
<button id="btn1">Insert before</button>
<button id="btn2">Insert after</button>
</body>
</html>

Remove Elements/Content

To remove elements and content, there are mainly two jQuery methods:
  • remove() - Removes the selected element (and its child elements)
  • empty() - Removes the child elements from the selected element

jQuery remove() Method

The jQuery remove() method removes the selected element(s) and its child elements.

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("#div1").remove();
  });
});
</script>
</head>
<body>

<div id="div1" style="height:100px;width:300px;border:1px solid black;background-color:yellow;">

This is some text in the div.
<p>This is a paragraph in the div.</p>
<p>This is another paragraph in the div.</p>

</div>
<br>
<button>Remove div element</button>

</body>
</html>

jQuery empty() Method

The jQuery empty() method removes the child elements of the selected element(s).
<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("#div1").empty();
  });
});
</script>
</head>
<body>

<div id="div1" style="height:100px;width:300px;border:1px solid black;background-color:yellow;">

This is some text in the div.
<p>This is a paragraph in the div.</p>
<p>This is another paragraph in the div.</p>

</div>
<br>
<button>Empty the div element</button>

</body>
</html>

Filter the Elements to be Removed

The jQuery remove() method also accepts one parameter, which allows you to filter the elements to be removed.
The parameter can be any of the jQuery selector syntaxes.
The following example removes all <p> elements with class="italic":  

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("p").remove(".italic");
  });
});
</script>
</head>
<body>

<p>This is a paragraph in the div.</p>
<p class="italic"><i>This is another paragraph in the div.</i></p>
<p class="italic"><i>This is another paragraph in the div.</i></p>
<button>Remove all p elements with class="italic"</button>

</body>
</html>

jQuery Manipulating CSS

jQuery has several methods for CSS manipulation. We will look at the following methods:
  • addClass() - Adds one or more classes to the selected elements
  • removeClass() - Removes one or more classes from the selected elements
  • toggleClass() - Toggles between adding/removing classes from the selected elements
  • css() - Sets or returns the style attribute

jQuery addClass() Method

The following example shows how to add class attributes to different elements. Of course you can select multiple elements, when adding classes:

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("h1,h2,p").addClass("blue");
    $("div").addClass("important");
  });
});
</script>
<style type="text/css">
.important
{
font-weight:bold;
font-size:xx-large;
}
.blue
{
color:blue;
}
</style>
</head>
<body>

<h1>Heading 1</h1>
<h2>Heading 2</h2>
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
<div>This is some important text!</div>
<br>
<button>Add classes to elements</button>

</body>
</html>

jQuery removeClass() Method

The following example shows how to remove a specific class attribute from different elements:

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("h1,h2,p").removeClass("blue");
  });
});
</script>
<style type="text/css">
.important
{
font-weight:bold;
font-size:xx-large;
}
.blue
{
color:blue;
}
</style>
</head>
<body>

<h1 class="blue">Heading 1</h1>
<h2 class="blue">Heading 2</h2>
<p class="blue">This is a paragraph.</p>
<p>This is another paragraph.</p>
<br>
<button>Remove class from elements</button>
</body>
</html>

jQuery toggleClass() Method

The following example will show how to use the jQuery toggleClass() method. This method toggles between adding/removing classes from the selected elements:

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("h1,h2,p").toggleClass("blue");
  });
});
</script>
<style type="text/css">
.blue
{
color:blue;
}
</style>
</head>
<body>

<h1>Heading 1</h1>
<h2>Heading 2</h2>
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
<button>Toggle class</button>
</body>
</html>












 




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