Javascript Basics Tutorial
JavaScript Objects
JavaScript Advanced
JavaScript Useful Resources
Selected Reading
- Javascript - Page Printing
- Javascript - Void Keyword
- Javascript - Dialog Boxes
- Javascript - Page Redirect
- Javascript - Cookies
- Javascript - Events
- Javascript - Functions
- Javascript - Loop Control
- Javascript - For...in
- Javascript - For Loop
- Javascript - While Loop
- Javascript - Switch Case
- Javascript - If...Else
- Javascript - Operators
- Javascript - Variables
- Javascript - Placement
- Javascript - Enabling
- Javascript - Syntax
- Javascript - Overview
- Javascript - Home
JavaScript Objects
- Javascript - HTML DOM
- Javascript - RegExp
- Javascript - Math
- Javascript - Date
- Javascript - Arrays
- Javascript - Strings
- Javascript - Boolean
- Javascript - Number
- Javascript - Objects
JavaScript Advanced
- Javascript - Browsers
- Javascript - Image Map
- Javascript - Debugging
- Javascript - Multimedia
- Javascript - Animation
- Javascript - Validations
- Javascript - Error Handling
JavaScript Useful Resources
- Javascript - Resources
- Javascript - Functions
- Javascript - Quick Guide
- Javascript - Questions And Answers
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
Javascript - Syntax
JavaScript - Syntax
JavaScript can be implemented using JavaScript statements that are placed within the <script>... </script> HTML tags in a web page.
You can place the <script> tags, containing your JavaScript, anywhere within your web page, but it is normally recommended that you should keep it within the <head> tags.
The <script> tag alerts the browser program to start interpreting all the text between these tags as a script. A simple syntax of your JavaScript will appear as follows.
<script ...> JavaScript code </script>
The script tag takes two important attributes −
Language − This attribute specifies what scripting language you are using. Typically, its value will be javascript. Although recent versions of HTML (and XHTML, its successor) have phased out the use of this attribute.
Type − This attribute is what is now recommended to indicate the scripting language in use and its value should be set to "text/javascript".
So your JavaScript segment will look pke −
<script language = "javascript" type = "text/javascript"> JavaScript code </script>
Your First JavaScript Code
Let us take a sample example to print out "Hello World". We added an optional HTML comment that surrounds our JavaScript code. This is to save our code from a browser that does not support JavaScript. The comment ends with a "//-->". Here "//" signifies a comment in JavaScript, so we add that to prevent a browser from reading the end of the HTML comment as a piece of JavaScript code. Next, we call a function document.write which writes a string into our HTML document.
This function can be used to write text, HTML, or both. Take a look at the following code.
<html>
<body>
<script language = "javascript" type = "text/javascript">
<!--
document.write("Hello World!")
//-->
</script>
</body>
</html>
This code will produce the following result −
Hello World!
Whitespace and Line Breaks
JavaScript ignores spaces, tabs, and newpnes that appear in JavaScript programs. You can use spaces, tabs, and newpnes freely in your program and you are free to format and indent your programs in a neat and consistent way that makes the code easy to read and understand.
Semicolons are Optional
Simple statements in JavaScript are generally followed by a semicolon character, just as they are in C, C++, and Java. JavaScript, however, allows you to omit this semicolon if each of your statements are placed on a separate pne. For example, the following code could be written without semicolons.
<script language = "javascript" type = "text/javascript">
<!--
var1 = 10
var2 = 20
//-->
</script>
But when formatted in a single pne as follows, you must use semicolons −
<script language = "javascript" type = "text/javascript">
<!--
var1 = 10; var2 = 20;
//-->
</script>
Note − It is a good programming practice to use semicolons.
Case Sensitivity
JavaScript is a case-sensitive language. This means that the language keywords, variables, function names, and any other identifiers must always be typed with a consistent capitapzation of letters.
So the identifiers Time and TIME will convey different meanings in JavaScript.
NOTE − Care should be taken while writing variable and function names in JavaScript.
Comments in JavaScript
JavaScript supports both C-style and C++-style comments, Thus −
Any text between a // and the end of a pne is treated as a comment and is ignored by JavaScript.
Any text between the characters /* and */ is treated as a comment. This may span multiple pnes.
JavaScript also recognizes the HTML comment opening sequence <!--. JavaScript treats this as a single-pne comment, just as it does the // comment.
The HTML comment closing sequence --> is not recognized by JavaScript so it should be written as //-->.
Example
The following example shows how to use comments in JavaScript.
<script language = "javascript" type = "text/javascript">
<!--
// This is a comment. It is similar to comments in C++
/*
* This is a multi-pne comment in JavaScript
* It is very similar to comments in C Programming
*/
//-->
</script>
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