array has index?

function hasIndex(array, index) {
    return array.splice(index, 1).reduce(function () {
        return true;
    }, false);
}

var array = [];
hasIndex(array, 0); // => false

array[0] = 1;
hasIndex(array, 0); // => true

array[0] = undefined;
hasIndex(array, 0); // => true

array[2] = 1;
hasIndex(array, 1); // => false