Perform a long computation with pauses between steps, for the UI to be able to render and not freeze.

longOperation.js

// Inspired from : http://www.sitepoint.com/multi-threading-javascript/
longOperation: function (fn, initData, interval) {
    var data = initData, busy = false;
    var result = $q.defer();
    var taskId;
    var task = function() {
        if(!busy) {
            busy = true;
            var res = fn(data);
            data = res.data;
            if (res.continueWhile === undefined) {
                throw new Error("Result doesn't define 'continueWhile' !");
            }
            if(!res.continueWhile) {
                clearInterval(taskId);
                result.resolve(data);
            }
            busy = false;
        }
    };

    return {
        run: function() {
            taskId = setInterval(task, interval);
            return result.promise;
        }
    };
}


// Example using Angular's $q for promises
var op = AsyncHelper.longOperation(function(data) {
    var a = data.array;
    var n = data.array.length;
    var i = data.i;
    var upBound = Math.min(i + data.step - 1, n);
    $log.info("from " + i + " to " + upBound);
    while (i < upBound) {
        for (var j = 0; j < 100; j++) {
            a[i++] += Math.floor(Math.random() * 10);
        }
    }
    return {
        data: {
            array: a,
            i: i+1,
            step: data.step
        },
        continueWhile: data.i < n
    };
}, {
    array: new Uint32Array(N),
    i: 0,
    step: Math.floor(N / 10)
}, 20);
op.run().then(function(data) {
    $log.info("final value : array[42] = " + data.array[42]);
});