Distance w/Pythagorean

distance_between_points.js

// I should have studied harder!
// http://en.wikipedia.org/wiki/Pythagorean_theorem
function distanceBetween(begin, end) {
    var xs = end.x - begin.x, ys = end.y - begin.y;
    return Math.sqrt(xs * xs + ys * ys);
}