In my continuing posts on operators, I would be remiss if I did not address a special one entitled, ‘Modulus’. Working with Modulus seems odd at first because it uses the percent (%) symbol. Plus, the name seems just plain weird doesn’t it? So what is modulus and how do we use it?

Modulus simply performs a division calculation and returns the remainder. Here is an example…

[code lang=”js”]

// Perform a modulus calculation

var modulusVar = 3 % 2;

document.write(modulusVar);

[/code]

If you run the aforementioned code, the result would be one (1). In other words, the value of the variable modulusVar would be 1. Why? Three divided by two leaves a remainder of one.

Okay…I can hear you now…”That is cool and all, but how useful is it?” Turns out very. The scenario where I have used modulus most often is testing whether a value is even or odd. I have done this to create alternate row styling on a table, etc. Here is an example…

[code lang=”js”]

// Perform a modulus calculation

var modulusVarOne = 3 % 2;

var modulusVarTwo = 4 % 2;

if(modulusVarOne === 0){

document.write("This is an even number");

} else {

document.write("This is an odd number");

}

if(modulusVarTwo === 0){

document.write("This is an even number");

} else {

document.write("This is an odd number");

}

[/code]

So you could take a variable where you perhaps have had your end user input a numeric value. You can then use modulus to divide by two and test even versus odd. If the remainder is zero (0), it is even. Anything else is odd.

Happy Coding!

Clay Hess