Chapter 5 Scripting Language Java Script n PHP
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Chapter 5 Scripting Language (Java Script ‘n’ PHP)
Scripting Language A high level programming language that is interpreted by another program at runtime rather than compiled by the computer's processor as other programming languages (such as C and C++) are. Scripting languages, which can be embedded within HTML, commonly are used to add functionality to a Web page, such as different menu styles or graphic displays or to serve dynamic advertisements. These types of languages are client-side scripting languages, affecting the data that the end user sees in a browser window. Other scripting languages are server-side scripting languages that manipulate the data, usually in a database, on the server. Scripting languages came about largely because of the development of the Internet as a communications tool. Java. Script, ASP, JSP, PHP, Perl, Tcl and Python are examples of scripting languages. Client-Side Script: generally refers to the class of computer programs on the web that are executed client-side, by the user's web browser, instead of serverside (on the web server). This type of computer programming is an important part of the Dynamic HTML (DHTML) concept, enabling web pages to be scripted; that is, to have different and changing content depending on user input, environmental conditions (such as the time of day), or other variables.
Client-side scripts are often embedded within an HTML or XHTML document (hence known as an "embedded script"), but they may also be contained in a separate file, to which the document that use it make reference (hence known as an "external script"). Upon request, the necessary files are sent to the user's computer by the web server on which they reside. The user's web browser executes the script, then displays the document, including any visible output from the script. Server-Side Script: written in languages such as PHP, ASP. NET, Java, Cold. Fusion, Perl, Ruby, Python, and server-side Java. Script, are executed by the web server when the user requests a document. They produce output in a format understandable by web browsers (usually HTML), which is then sent to the user's computer. The user cannot see the script's source code and may not even be aware that a script was executed. Documents produced by serverside scripts may, in turn, contain client-side scripts. Server-side scripts require that their language's interpreter be installed on the server, and produce the same output regardless of the client's browser, operating system, or other system details. Client-side scripts do not require additional software on the server; however, they do require that the user's web browser understands the scripting language in which they are written. It is therefore impractical for an author to write scripts in a language that is not supported by popular web browsers.
Java. Script is a simple, powerful, and popular programming language that is built into web browsers. Learning Java. Script is especially useful if you are a web designer and already know HTML and CSS, because it is used to make web pages interactive. However, Java. Script is not limited to making interactive web pages; you can also use it for server-side programming using a framework like Node. js. Java. Script programs are a sequence of statements or commands that are run by a web browser in the order they are written. The code below is an example of a Java. Script Hello World program wrapped in a few lines of HTML, which enables it to run in a web browser as a valid web page: <!doctype html> <title>Java. Script Test</title> <script> alert('Hello World!'); </script> In the example above, the Java. Script code is the line between the <script> and </script>. This line contains a Java. Script alert command that instructs the web browser to display a message box that contains the text between the quotation marks.
Common Scripting Tasks 1. Adding dynamic features to Web pages • validation of form data • image rollovers • time-sensitive or random page elements • handling cookies 2. Defining programs with Web interfaces • utilize buttons, text boxes, clickable images, prompts, frames limitations of client-side scripting § since script code is embedded in the page, viewable to the world § for security reasons, scripts are limited in what they can do e. g. , can't access the client's hard drive § since designed to run on any machine platform, scripts do not contain platform specific commands § script languages are not full-featured e. g. , Java. Script objects are crude, not good for large project development
How to run a script program: • Write the code in a text editor (such as Dreamweaver or Notepad). • Save the file as filename. html • Open the file using your favorite web browser. • If you'd like, you can edit test. html to change the message that appears in the message box, then save your code and click F 5 while your web browser is active to refresh the page.
How does it work? • Embedded within HTML page. • Executes on client. • Simple programming statements combined with HTML tags. • Interpreted (not compiled), No special tools required. Java. Script Statements <html> <head><title>My Page</title></head> <body> <script language="Java. Script"> document. write('<h 1>This is my first Java. Script Page</h 1>'); </script> </body> </html> HTML written inside Java. Script
Java Script Statements <html> <head><title>My Page</title></head> <body> <p> <a href="myfile. html">My Page</a> <a href="myfile. html" on. Mouseover="window. alert('Hello'); "> My Page</A> </p> </body> </html> Java. Script written An Event inside HTML
Example Statements <script language="Java. Script"> window. prompt('Enter your name: ', ''); </script> Another event <form> <input type="button" Value="Press" on. Click="window. alert('Hello'); "> </form> Note quotes: " and '
HTML Forms and Java. Script • Java. Script is very good at processing user input in the web browser • HTML <form> elements receive input • Forms and form elements have unique names • Each unique element can be identified • Uses Java. Script Document Object Model (DOM) Naming Form Elements in HTML <form name="addressform"> Name: <input name="yourname"> Phone: <input name="phone"> Email: <input name="email"> </form>
Forms and Java. Script document. formname. elementname. value Thus: document. addressform. yourname. value document. addressform. phone. value document. addressform. email. value
Using Form Data <form name="alertform"> Enter your name: <input type="text" name="yourname"> <input type="button" value= "Go" on. Click="window. alert('Hello ' + document. alertform. yourname. value); "> </form>
Introduction to PHP • PHP is server side scripting system. • PHP stands for "PHP: Hypertext Preprocessor“. • Syntax based on Perl, Java, and C. • Very good for creating dynamic content. • Powerful, but somewhat risky! • If you want to focus on one system for dynamic content, this is a good one to choose. PHP Scripts • Typically file ends in. php--this is set by the web server configuration. • Separated in files with the <? php ? > tag. • php commands can make up an entire file, or can be contained in html. • Program lines end in "; " or you get an error. • Server recognizes embedded script and executes. • Result is passed to browser, source isn't visible. <P> <? php $myvar = "Hello World!"; echo $myvar; ? > </P>
How it works: PHP code is executed on the server, generating HTML which is then sent to the client. The client would receive the results of running that script, but would not know what the underlying code was. A visual, if you please. . .
PHP Getting Started • On windows, you can download and install WAMP. With one installation and you get an Apache webserver, database server and php. • http: //www. wampserver. com • On mac, you can download and install MAMP. • http: //www. mamp. info/en/index. html Above is the PHP source code. It renders as HTML that looks like this.
PHP Variables • Variables are used for storing values, like text strings, numbers or arrays. • When a variable is declared, it can be used over and over again in your script. • All variables in PHP start with a $ sign symbol. • The correct way of declaring a variable in PHP: • In PHP, a variable does not need to be declared before adding a value to it. • In the example above, you see that you do not have to tell PHP which data type the variable is. • PHP automatically converts the variable to the correct data type, depending on its value.
PHP Conditional Statements • If statement - use this statement to execute some code only if a specified condition is true. • If. . . else statement - use this statement to execute some code if a condition is true and another code if the condition is false. • If-elseif-else statement - use this statement to select one of several blocks of code to be executed. • Switch statement - use this statement to select one of many blocks of code to be executed.
PHP Arrays In PHP, there are three kind of arrays: • Numeric array - An array with a numeric index. • Associative array - An array where each ID key is associated with a value. • Multidimensional array - An array containing one or more arrays. In the following example you access the variable values by referring to the array name and index: The code above will output:
PHP Loops • while - loops through a block of code while a specified condition is true. • do. . . while - loops through a block of code once, and then repeats the loop as long as a specified condition is true. • for - loops through a block of code a specified number of times. • foreach - loops through a block of code for each element in an array. A while loop example: