Javascript JavaScript is what is called a client-side scripting language:  a programming language that runs inside an Internet browser (a browser is also known as a Web client because it connects to a Web server to download pages)‏ Inside a normal Web page you place some JavaScript code. When the browser loads the page, the browser has a built-in interpreter that reads the JavaScript code it finds in the page and runs it.

Possible Usage Web page designers use JavaScript in many different ways:  One of the most common is to do field validation in a form. Many Web sites gather information from users in online forms, and JavaScript can help validate entries. For example, the programmer might validate that a person's age entered into a form falls between 1 and 120.  Another way that web page designers use JavaScript is to create calculators.

Simple Calculator (1) The HTML below shows you how to create a Fahrenheit to Celsius converter using JavaScript: function temp(form) { var f = parseFloat(form.DegF.value, 10); var c = 0; c = (f ) * 5.0 / 9.0; form.DegC.value = c; }

Simple Calculator (2) In the body of the page there is a typical form: Fahrenheit to Celsius Converter Enter a temperature in degrees F: Click this button to calculate the temperature in degrees C: <INPUT NAME="calc" VALUE="Calculate" TYPE=BUTTON onClick=temp(this.form)> Temperature in degrees C is: