const o = {}; o.Foo = 'bar'; o.Baz = 42.0001; o.Blah = o.Foo + o.Baz; if(o.Blah != 'bar42.0001') throw TypeError; const fib = n => { if(n<2) { return n; } return fib(n-1) + fib(n-2); }; if(fib(3) != 2) throw TypeError;