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Essential Javascript -- A Javascript Tutorial

By Patrick Hunlock
2007-12-02


Output (writeln)

One of the most important things to do when learning a new language is to master basic input and output which is why hello world has become almost a cliche in programming textbooks. For Javascript you need three hello worlds because there are three ways to communicate with the user, each increasingly more useful than the last.

The first method is to use the document.writeln(string) command. This can be used while the page is being constructed. After the page has finished loading a new document.writeln(string) command will delete the page in most browsers, so use this only while the page is loading. Here's how a simple web-page will look... 

<html>
  <head>
  </head>
  <body>
     <script type='text/javascript'>

        document.writeln('Hello World!');     

     </script>
  </body>
</html>

As the page is loading, Javascript will encounter this script and it will output "Hello World!" exactly where the script block appears on the page.

The problem with writeln is that if you use this method after the page has loaded the browser will destroy the page and start constructing a new one. As you can see by clicking on this example which will execute a document.writeln after the page has finished loading.

For the most part, document.writeln is useful only when teaching yourself the language. Dynamic content during page load is better served by the server-side scripting languages. That said, document.writeln is very useful in pre-processing forms before they're sent to the server -- you can basically create a new web-page on the fly without the need to contact the server.



Tutorial Pages:
» Essential Javascript -- A Javascript Tutorial
» Getting Started
» In-Line Javascript
» External Javascript
» Javascript is case sensitive
» Output (writeln)
» Output (alert)
» Output (getElementById)
» Input (One Click To Rule Them All)
» Input (User Input)
» Javascript is an Event Driven Language
» Comments
» Variables
» Variable Scope
» Special Keywords
» Arithmetic Operators
» Logical and Comparison Operators
» JavaScript Conditionals: IF
» JavaScript Conditionals: SWITCH
» JavaScript Conditionals: Shorthand Assignment
» JavaScript Conditionals: Ternary Operators
» JavaScript Loops: FOR
» JavaScript Loops: FOR/IN
» JavaScript Loops: WHILE
» Bringing It All Together
» DHTML: Dynamic HTML
» Conclusion


copyright © 2006, 2007 by Patrick Hunlock

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Related Tutorials:
» JavaScript Debugging Techniques with Firebug
» Striped Tables Using JavaScript
» Opening PDFs in a New Window with JavaScript
» Submit Forms Conditionally using JavaScript
» How to Setup a Randomising Function
» Introduction to JavaScript Tutorial

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