Unhelpful error messages

[joydeep-b]

[1, 2, 3,4].find(4) 
pred is not a function at Line 278: in (anonymous function)

This should be fixed with a dyn type check

[joydeep-b]

class Dog {
  constructor(leash) {
  }
};

let d = new Dog();

Produces:

function (anonymous) expected 1 argument but received 0 arguments at Line 2: in Dog
... : in handleNew
... 

The handleNew bit is an internal (Stopify) leaking through.

[sp1tz]

Partitioned into atomic issues #184 & #185.