Arrow function with inner function fails to parse

[pimlie]

The following snippet fails to parse because result.value is erroneously(?) wrapped in { ... } on line https://github.com/tunnckoCoreLabs/parse-function/blob/master/src/index.js#L119-L121

import parseFunction from 'parse-function'
parseFunction().parse(arg => new Promise(resolve => {
    function inner() {}
    inner()
}))

babylon / @babel/parser throws the following error:

    SyntaxError: Unexpected token, expected "," (1:6)

      at Parser.raise (node_modules/babylon/lib/index.js:776:15)
      at Parser.unexpected (node_modules/babylon/lib/index.js:2079:16)
      at Parser.expect (node_modules/babylon/lib/index.js:2067:28)
      at Parser.parseObj (node_modules/babylon/lib/index.js:3465:14)
      at Parser.parseExprAtom (node_modules/babylon/lib/index.js:3123:21)
      at Parser.parseExprSubscripts (node_modules/babylon/lib/index.js:2757:21)
      at Parser.parseMaybeUnary (node_modules/babylon/lib/index.js:2736:21)
      at Parser.parseExprOps (node_modules/babylon/lib/index.js:2643:21)
      at Parser.parseMaybeConditional (node_modules/babylon/lib/index.js:2615:21)
      at Parser.parseMaybeAssign (node_modules/babylon/lib/index.js:2562:21)

Maybe just add isArrow to the if on line 119? Or might that cause problems with arrow functions in normal function bodies because the includes('=>') is too greedy and should only look at the start?

[tunnckoCore]

Thanks for the report.

Interesting, I'll look on it.

[tunnckoCore]

For some reason, wrapping it as string works.

import parseFunction from 'parse-function';

const res = parseFunction().parse(
  `(arg, bar) =>
    new Promise((resolve) => {
      function inner() {}

      inner();
    })`,
);

console.log(res);
/*
{ name: null,
  body:
   'new Promise((resolve) => {\n      function inner() {}\n\n      inner();\n    })',
  args: [ 'arg', 'bar' ],
  params: 'arg, bar' }
*/

[tunnckoCore]

Actually, forget that. When I initially pasted it and executed it really it failed. But when it is formatted, your snippet works too.

import parseFunction from 'parse-function';

parseFunction().parse(
  (arg) =>
    new Promise((resolve) => {
      function inner() {}
      inner();
    }),
);

Does not fail. But you are kind of right, it's probably something with the wrapping. But it's done that way because we use .parseExpression.

This works too

parseFunction().parse(arg => {
  return new Promise(resolve => {
    function inner() {}
    inner();
  });
});

but this doesn't

parseFunction().parse(arg => new Promise(resolve => {
    function inner() {}
    inner();
  });
);

So, please use Eslint and/or Prettier.

[pimlie]

Thanks for the quick update. Actually I am using eslint already and it didnt report anytning because it has 'arrow-parens': [2, 'as-needed', { requireForBlockBody: true }], set and the rule doesnt think I need a block'ed body I guess.
-- edit --
hmm sorry, this rule is about () around the args ofc. I extend some other configs, will have a look at them what they do
-- /edit --

Really strange adding a linebreak works, from all the things I did to debug this thats one of the only things I didnt try ;)

Just wondering, if it is about the new Promise expression I would've expected the following to work too (but it doesnt):

parseFunction().parse(arg => (new Promise(resolve => {
    function inner() {}
    inner();
  }));
);

[tunnckoCore]

@pimlie yea, I'm not sure why it is happening too. I have a pretty big eslint config, so I'm not sure if ESLint-only approach will help either. That's one of the things why Prettier is amazing.

It's kinda strange because it's perfectly valid javascript.

'use strict'

const foo = arg => new Promise(resolve => {
    function inner() {}
    inner()
})

foo(123)