Keep track of how much time is spent showing certain elements on the page

Question

So lets say we have 4 Divs (3 hidden, 1 visible), the user is able to toggle between them through javascript/jQuery.

I want to calculate time spent on each Div, and

Answer 1

Here is a reusable class, example is included in code:

/*
     Help track time lapse - tells you the time difference between each "check()" and since the "start()"

 */
var TimeCapture = function () {
    var start = new Date().getTime();
    var last = start;
    var now = start;
    this.start = function () {
        start = new Date().getTime();
    };
    this.check = function (message) {
        now = (new Date().getTime());
        console.log(message, 'START:', now - start, 'LAST:', now - last);
        last = now;
    };
};

//Example:
var time = new TimeCapture();
//begin tracking time
time.start();
//...do stuff
time.check('say something here')//look at your console for output
//..do more stuff
time.check('say something else')//look at your console for output
//..do more stuff
time.check('say something else one more time')//look at your console for output