JavaScript® Bible, Seventh Edition

Chapter 56. Application: Calculations and Graphics

IN THIS CHAPTER

• Pre-cached images

• Math calculations

• CGI-like image assembly

When the scripting world had its first pre-release peeks at JavaScript (while Netscape was still calling the language LiveScript), the notion of creating interactive HTML-based calculators captured the imaginations of many page authors. Somewhere on the World Wide Web, you can find probably every kind of special-purpose calculation normally done by scientific calculators and personal computer programs—leaving only weather-modeling calculations to the supercomputers of the world.

In the search for my calculator gift to the JavaScript universe, I looked around for something more graphical. Numbers, by themselves, are pretty boring; so any way the math could be enlivened was fine by me. Having been an electronics hobbyist since I was a kid, I recalled the color-coding of electronic resistor components. The values of these gizmos aren't printed in plain numbers anywhere. You have to know the code and the meaning of the location of the colored bands to arrive at the value of each one. I think that this calculator will be fun to play with, even if you don't know what a resistor is.

The Calculation

To give you an appreciation for the calculation that goes into determining a resistor's value, here is the way the system works. Colored bands are printed on the surface of a resistor to encode its resistance value in ohms. The first (leftmost) band is the tens digit; the second ...