Existing functionality is maintained using toString. This is necessary to
support type checking, and to be more consistent with the native Symbol
implementation.
Technically `new FallbackSymbol` is supposed to throw a TypeError, just as
`new Symbol` would, but doing so complicates the constructor unncessarily,
so I am not going to bother with that here.
This is the closest we will get to implementing a concept similar to symbols
in pre-ES6. The intent is that, in an ES5 environment, the caller should
ensure that the object receiving this key will mark it as non-enumerable.
Otherwise, we're out of luck.
The symbol string is pseduo-randomly generated with an attempt to reduce the
likelihood of field collisions and malicious Math.{floor,random} overwrites
(so long as they are clean at the time of loading the module).
During its initial development, no environments (e.g. Node.js, Chromium,
Firefox) supported strict mode; this has since changed, and node has a
--use-strict option, which is used in the test runner to ensure conformance.
The parser methods are now split into their own functions. This has a number
of benefits: The most immediate is the commit that will follow. The second
benefit is that the function is no longer a closure---all context
information is passed into it, and so it can be optimized by the JavaScript
engine accordingly.
Mike Gerwitz