Another Odd Question...

Hello Digital Point,

I was reading my JavaScript book the other day... it shows an 'Bingo Card' question/example but the book does not really explain the logic behind question/example. I typed it in several times today trying to grasp the logic... but I do not get the logic so I need an explanation of how it works...

window.onload = newCard;

function newCard() {
	if (document.getElementById) {
		for (var i=0; i<24; i++) {
			setSquare(i);
		}
	}
	else {
		alert("Sorry, your browser doesn't support this script");
	}
}

function setSquare(thisSquare) {
	var currSquare = "square" + thisSquare;
	var colPlace = new Array(0,1,2,3,4,0,1,2,3,4,0,1,3,4,0,1,2,3,4,0,1,2,3,4);
	var newNum = (colPlace[thisSquare] * 15) + Math.floor(Math.random() * 15) + 1;

	document.getElementById(currSquare).innerHTML = newNum;
}

Code (markup):

I understand the functions, methods, and parameters work... but this is the line of code that causing my confusion.

var newNum = (colPlace[thisSquare] * 15) + Math.floor(Math.random() * 15) + 1;

Code (markup):

 

The script is filling in the bingo card by rows and columns. The line of code you ask about generates a random number based on 15 times the column plus a random number between 1 and 15. The purpose is to create a bingo card with numbers that fall within a specific range in each column.

 

So does it work like?...