title: Vanilla JS assertion lib alternative to Meteor's check package
body: <p>The application framework Meteor has a package called <code>check</code> that can be used to <a href="http://docs.meteor.com/#matchpatterns" rel="nofollow">assert boundaries on your inputs</a>, and related stuff. This is really kind of nifty, and very useful to have easy ways of checking that a string conforms to say ISO8601 or that an object contains certain fields.</p>
  
  <p>Unfortunately this is a Meteor specific package, and I would like to have something similar for standalone use in vanilla js. Any alternatives worth mentioning?</p>