Iterate through series of timers I wrote a short program for my exercise routine. It takes a JSON array of exercise names and duration (seconds) and puts it on the screen. The JSON looks like this:

var exerciseArray = [
    {
        "desc":       "Pushup/Pullup",
        "countdown":  30
    }, {
        "desc":       "Squat punch",
        "countdown":  45
    }, {
        "desc":       "Jumping jacks",
        "countdown":  60
    }
];


The function works, but it seems to be to be kind of a kludge. My problem was that I couldn't figure out how work with setInterval to iterate through the list of exercises (exerciseArray). What I did in the end is just decrement the countdown value, and when it's zero, move to the next item in exerciseArray (i++;). When I hit the end of the array — as measured by i and exerciseArray.length — I just run clearInterval and I'm done. Code below (I removed some of the extraneous stuff that just updates the HTML with the number of seconds, you can see the full thing on github):

function exerciseTimer(exerciseArray) {
    var i = 0;
    var exerciseObject = exerciseArray[i];
    // do stuff
    var tt = setInterval(function() {
        var exerciseObject = exerciseArray[i];
        // write html to the page
        exerciseObject.countdown = exerciseObject.countdown - 1;
        if (exerciseObject.countdown &lt;= 0) { 
            if(i &lt; (exerciseArray.length - 1)) {
                i++;
            } else {
                clearInterval(tt);
            }
        }
    }, 100);
}


My question is, what is the appropriate way to iterate while using setInterval? Is there a cleaner way? This feels very ugly to me.
If you only need the entries once, you could simply keep using shift until there are no more entries:

var exercises = [
    {
        "desc":       "Pushup/Pullup",
        "countdown":  30
    }, {
        "desc":       "Squat punch",
        "countdown":  45
    }, {
        "desc":       "Jumping jacks",
        "countdown":  60
    }
];

function exerciseTimer(exercises) {
    // do stuff
    var exercise = exercises.shift(),
        tt = setInterval(function() {
            // write html to the page
            exercise.countdown = exercise.countdown - 1;
            //Does it work ?
            console.log( exercise );
            if (exercise.countdown &lt;= 0) { 
                exercise = exercises.shift(); 
                if(!exercise) {
                    clearInterval(tt);
                }
            }
        }, 100);
    };

exerciseTimer( exercises );


I would also suggest to not make the type of the variable part of the variable name. exercise and exercises are much easier to read than exerciseArray and exerciseObject.