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loop: function(cb) {
    var intervalId;

    var cycle = function() {
        var ret = cb();

        if(ret == false) {
            clearInterval(intervalId);
        }
    }

    intervalId = setInterval(cycle, 0);
}

...
// let's do some work with our interval based loop
var isProcessing = true;

loop(function() {
    if(isProcessing) {
        // do some work now    

        // remember to set isProcessing to false at some point
        // note that you can replace it with any other sort of condition as well...
        isProcessing = false;

        // add progress cb here if you want to

        return true; // let's continue executing the loop
    }

    // add done cb here if you want to

    return false; // we're done, let's get outta here
});

function process(progressCb, readyCb) {
    var isProcessing = true;
    var intervalId;

    var exec = function() {
        if(isProcessing) {
            // do some processing now, set isProcessing to false once you are done
            ...
            
            // pass progress status here if you want to
            progressCb();
        }
        else {
            // time to kill the interval. you served us well
            clearInterval(intervalId);
            
            readyCb();
        }
    }

    // execute interval as often as possible, hence zero
    intervalId = setInterval(exec, 0);
}