Bad Bar Joke
A man walks into a bar with a sandwich on his shoulder.

The bartender turns, looks at him and says, ''Sorry sir, we don't serve food here!!''

Basic Calculation Tutorial
A great thing for beginners to do is to make a simple calculation script. It teaches them how to reference form elements, use basic math functions, and display information to the user. Here is a simple tutorial to do a calculation between a field and display the result.

In this example, we are going to calculate the tax rate on an item purchased. Basically it is a simple multiplication problem.

First you need to create a form where the user can enter in a value. We need a textbox and a button to perform the calculation when clicked. The button needs an onclick event handler added to it and call a function MyCalc() which we will make in a bit.

<form name="Form1">
  $<input type="text" name="textTotal">
  <input type="button" name="btnCalc" value="Calculate Tax" onclick="MyCalc()">
</form>

Now we need to build a function called MyCalc(). This function gets called when you click the button.

<script type="text/javascript">
  function MyCalc(){
  }
</script>

You then need to reference the value in the text box, you do this by referencing the form object.

    var val1 = document.formName.elementName.value;

After that we need to do our calculation. You need to parseFloat to turn the form element value from a string to a number. The reason is if you were to an addition, it would join together instead of increasing in value. For example, two strings added together would equal "2" + "2" = 22 instead of 2 + 2 = 4.

    var amt = 1.06 * parseFloat(val1);

The last step is to display a total, for this we will use an alert.

    alert("Your total is $" + amt); 

Putting it all together it looks like:

<script type="text/javascript">
  function MyCalc(){
    var val1 = document.formName.elementName.value;
    var amt = 1.06 * parseFloat(val1);
    alert("Your total is $" + amt); 
  }
</script>

Hope that helps you understand a basic JavaScript application.

Eric Pascarello
Moderator of HTML/JavaScript at www.JavaRanch.com
Author of: JavaScript: Your Visual Blueprint for Dynamic Web Pages