fix(cli/repl): interpret object literals as expressions

[caspervonb]

This wraps object literals in parenthesis so that they're interpreted as expressions rather than block statements which matches the behaviour of Node and web-browsers.

Fixes #1421

[caspervonb]

Old behavior has some interesting edge cases

Master:

This pull request:

[nayeemrmn]

Fixes #1421. I suppose this is better even if block statements can't be used.

[kitsonk]

The existing behaviour is consistent with Node.js. Is there compelling reason to vary from that?

[lucacasonato]

The existing behaviour is consistent with Node.js. Is there compelling reason to vary from that?

It is not.

[kitsonk]

Ah, but { "" } does not throw a syntax error though.

[kitsonk]

Also, { "" } in the dev console in Chrome doesn't throw either. It returns "".

Maybe a RegEx that is a bit more specific in looking for things that look like an object literal but ignores things that couldn't be an object literal. The following:

/^\s*{\s*(?:\S+|["'][^"']+["']):.+}\s*$/

Matches:

{ "foo": bar }
{ 'foo bar': bar }
{ [foo]: bar }

But ignores:

{ "" }

It isn't perfect, but it is really hard to make it perfect because of the lack of back references in JavaScript.

[caspervonb]

The existing behaviour is consistent with Node.js. Is there compelling reason to vary from that?

Node does the same, but with a different pattern match.

Also, { "" } in the dev console in Chrome doesn't throw either. It returns "".

Throws in Safari, not sure about Firefox (not installed at the moment).

/^\s*{\s*(?:\S+|["'][^"']+["']):.+}\s*$/

Yeah that regex is going to be pretty hard to get right, it should allow for non-quoted keys, but non-quoted keys look like labels, et cetera.

I think it might be better to have a rollback mechanism, e.g if our preprocessed code turned out to be a syntax error, do it again without the preprocessing.

[caspervonb]

Slightly more forgiving approach that leaves the parsing up to the compiler; if it looks like it might be an object literal we try it as an expression first, if thats a compile error we rollback and retry with the raw original code.

[ry]

Cool - nice hack.