Module 7: Accessing DOM with JavaScript презентация

Module 7: Accessing DOM with JavaScript

Agenda Introducing DOM Manipulating DOM with JavaScript Cookies and Storages Useful links

Introducing DOM

What is "DOM"? DOM – an acronym for Document Object Model. It's an interface that provides browser to allow scripts on a webpage to dynamically access and update the content, structure and style of documents. When browser prepares webpage to be shown to user, it constructs tree of objects from all elements of a page according to it's HTML structure JavaScript code can access the tree and modify it, browser reacts on changes and updates HTML page shown to the user. Changing HTML with JavaScript using DOM interface is also called as Dynamic HTML.

DOM Tree

What DOM Defines?

What can do JavaScript with DOM?

Manipulating DOM with JavaScript

Finding Elements

Finding HTML Elements by id var t = document.getElementById('target'); Will find one element with id "target"

Finding HTML Elements by Tag Name var p = document.getElementsByTagName('p'); Will find all paragraphs on a page

Finding HTML Elements by Class Name var p = document.getElementsByClassName('target'); Will find all elements with class 'target' on a page

Changing HTML

Changing HTML Content document.getElementById(id).innerHTML = New value Will replace inner content of an element

Changing the Value of an Attribute document.getElementById(id).attribute = New value Will replace inner content of an element

Changing HTML Style document.getElementById(id).style.property = New value Will replace inner content of an element

Using Events A JavaScript can be executed when an event occurs, examples of HTML events: When a user clicks the mouse When a user strokes a key When a web page has loaded When an image has been loaded When the mouse moves over an element When an input field is changed When an HTML form is submitted

Sample onclick() Event Handler

Cookies and Storages

What are Cookies? Cookies are data, stored in small text files, on client computer. There is a problem: when a web server has sent a web page to a browser, the connection is shut down, and the server forgets everything about the user. Cookies were invented to solve the problem: When a user visits a web page, his ID can be stored in a cookie. Next time the user visits the page, the cookie "remembers" his ID

Create a Cookie with JavaScript JavaScript can create, read, and delete cookies with the document.cookie property. A cookie can be created like this: document.cookie = "ID=123456789"; To save the cookie between browser sessions, we may add expiry date: document.cookie = "ID=123456789; expires=Wed, 01 Jul 2015 12:00:00 GMT"; By default, cookie belongs to the page that created it, path parameter allows to set what path the cookie belong to: document.cookie = "ID=123456789; expires=Wed, 01 Jul 2015 12:00:00 GMT; path=/";

Read a Cookie To read a cookie: var x = document.cookie; This code will return all cookies in one string in name=value pairs To find the value of one specified cookie, we must write a JavaScript function that searches for the cookie value in the cookie string.

Changing and Deleting Cookie Changing cookie is made same way as creating it: document.cookie = "ID=123456789; expires=Wed, 01 Jul 2015 12:00:00 GMT; path=/"; To delete a cookie we have to set expires parameter to a passed date: document.cookie = "ID=123456789; expires=Thu, 01 Jan 1970 00:00:00 GMT";

Sample Function to Set a Cookie The parameters of the function above are the name of the cookie (cname), the value of the cookie (cvalue), and the number of days until the cookie should expire (exdays). The function sets a cookie by adding together the cookiename, the cookie value, and the expires string.

Sample Function to Get a Cookie Take the cookiename as parameter (cname). Create a variable (name) with the text to search for (cname + '='). Split document.cookie on semicolons into an array called ca (ca = document.cookie.split(';')). Loop through the ca array (i=0;i<ca.length;i++), and read out each value trimmed (c=ca[i].trim()). If the cookie is found (c.indexOf(name) == 0), return the value of the cookie (c.substring(name.length,c.length). If the cookie is not found, return ''.

HTML5 Web Storage With HTML5, web pages can store data locally within the user's browser alternatively to cookies. Web Storage is more secure and faster. The data is not included with every server request, but used only when asked for. The data is stored in name/value pairs, and a web page can only access data stored by itself. Unlike cookies, the storage limit is far larger (at least 5MB) and information is never transferred to the server.

HTML5 Web Storage Objects

Initial Check Before using web storage, check browser support for localStorage and sessionStorage:

Using Storage Objects There are methods to use storage objects: .setItem() – writes data .getItem() – reads data Methods are identical for localStorage and sessionStorage

Sample Use of localStorage

Useful links

Useful Links HTML DOM на сайті Wikipedia: http://en.wikipedia.org/wiki/Document_Object_Model W3Schools JavaScript HTML DOM: http://www.w3schools.com/js/js_htmldom.asp Специфікація HTML DOM на сайті W3C: http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407/

Thank you!