Creating dummy data

The first thing it does is that it creates some dummy data. This is the data that determines how many rectangles to render, and how large the rectangles will be:

var rectangleWidth = 100, 
    data = [], 
    numberOfRectangles = Math.ceil(Math.random() * 7); 
 
for (var i = 0 ; i < numberOfRectangles ; i++) { 
    data.push((Math.random() * rectangleWidth / 2) 
                             + rectangleWidth / 2); 
}

This is just plain JavaScript, and this will result in the data array being filled with one to seven numeric values ranging from 50 to 100. It could look something like this:

[52.653238934888726, 88.52709144102309, 81.70794256804369, 58.10611357491862]