Some helpful validators about koa-validate

[RHavar]

I don't particularly see the need for the not api.

I propose two additional functions though:
ensureFn :: Takes a function, calls it with the value
ensureYield :: Takes a generator, calls it with the value and yields it.

Simple example:

this.checkBody('username').trim().ensureYield(db.userExists)  // yields db.userExists function with username
this.checkBody('address').trim().ensureFn(isValidBitcoinAddress) // calls sync function with the address value

[danneu]

I don't think ensureYield is general enough at first glance, but I like the idea of piping the value through a function. I'll play with it.

Also, ensureNot is useful because negating a yield is annoying. You have to wrap the whole expression in parens.

this.checkBody('uname').ensure(!(yield db.findUserByUname(this.request.body.uname)))
this.checkBody('uname').ensureNot(yield db.findUserByUname(this.request.body.uname)) // nicer

Sure, not a big deal, but this library already has a precedent for not in its API.

[RocksonZeta]

yeah, very powerful! happy Chinese new year!