Programming  with
JavaScript
Creating a Programmable Web Page

JavaScript Resources on the Web

Ask the JavaScript Pro
DevEdge Javascript Reference
Joy of JavaScript, A Companion Site for
   Javascript for the World Wide Web, Visual Quickstart
   Guide, 3rd Edition, by Tom Negrino and Dori Smith
JavaScript World
JavaScript Forum
The JavaScript Planet
JavaScript Resources
JavaScript World
JavaScript WebRing
Netscape's JavaScript Guide
ProjectCool: JavaScript Zone

Comparison Operators

variable = (condition) ? value1 : value2;

where variable is the variable name, condition is a conditional expression that is either true or false, value1 is the value of the variable if the condition is true, and value2 is the value if the condition is false. For example, the following JavaScript command:

Days = (Month=="Feb") ? "< 30" : ">= 30";

The variable Days will be equal to "< 30" if the Month variable is "Feb", otherwise it will be equal to ">= 30".

Interrupting Loops

The break command halts the loop, even if the conditions to the end the loop have not been met. For example, if you want to create a loop that prompts students to answer a question, and give them three chances to answer that question, you can use the following JavaScript program:

for (i=1;i<=3;i++) {

  answer=prompt("In what year did 

  the Civil War begin?","");

      if (answer=="1861") {

     alert("Correct answer");

   break;

  }<

}

In this example, if the answer variable is equal to "1861" (the correct answer) the loop stops with the break command. If the student answers the question incorrectly, the loop continues for 3 iterations or until the question is answered correctly (note that you can learn more about the alert() and prompt() methods in Tutorial 8.) To see this JavaScript program in action, click the button below:

Extending Strings with the += Operator

<SCRIPT>
var quote = "Be not afraid: the isle is full of noises, ";
quote+="sounds and sweet airs that give delight and hurt not. ";
quote+="Sometimes a thousand twangling instruments will hum ";
quote+="about mine ears; and sometime voices that, ";
quote+="if I then had waked after long sleep; ";
quote+="will make me sleep again; and then, in dreaming, ";
quote+="the clouds methought would open and show riches ready ";
quote+="to drop upon me, that, when I waked, ";
quote+="I cried to dream again. ";
document.write(quote);
</SCRIPT>

Here is the output from that script:

Be not afraid: the isle is full of noises, sounds and sweet airs that give delight and hurt not. Sometimes a thousand twangling instruments will hum about mine ears; and sometime voices that, if I then had waked after long sleep will make me sleep again; and then, in dreaming, the clouds methought would open and show riches ready to drop upon me, that, when I waked, I cried to dream again.

Notice that by using the += operator, you've created a text string much longer than the length of a single line.

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