Use

This package is used by can-define (and eventually can-observe) to define types. These types include a getSchema that enables them to be converted to can-query-logic set types.

import {DefineMap, MaybeDate, MaybeString, MaybeNumber} from "can";

const Todo = DefineMap.extend({
    id: MaybeNumber,
    name: MaybeString,
    dueDate: MaybeDate
});