counter.js

function count(seed, d) {
    var i = seed;
    return function counter(n) {
        i += (n || d);
        return function () {
            return i;
        };
    };
}
var i = count(1, 2);
console.assert(i()() === 3);
console.assert(i()() === 5);
/**/
function range(seed, limit, d) {
    var i = seed;
    return function counter(n) {
        i += (n || d);
        return i > limit ? null : function () {
            return i;
        };
    };
}
var inc = range(1, 10, 2);