Strange parser error when an if statement is at the top of an async arrow function

[TooTallNate]

Apologies if this is not a bug in parse-function itself, but I've tried this with all 3 recommended AST parsers and they all exhibit the same problem.

A parser error is thrown when an async arrow function has an if statement at the top. Ex:

$ cat t.js
const parser = require('parse-function')()

const fn = async (req, res) => {
  if (req) {}
}

console.log(parser.parse(fn));

$ node t
/test/node_modules/parse-function/node_modules/babylon/lib/index.js:812
    throw err;
    ^

SyntaxError: Unexpected token, expected { (1:19)

Strangely, the same error is thrown even if the if statement is commented out!

$ cat t.js
const parser = require('parse-function')()

const fn = async (req, res) => {
  //if (req) {}
}

console.log(parser.parse(fn));

$ node t
/test/node_modules/parse-function/node_modules/babylon/lib/index.js:812
    throw err;
    ^

SyntaxError: Unexpected token, expected { (1:19)

Now, it works if I remove the if statement:

$ cat t.js
const parser = require('parse-function')()

const fn = async (req, res) => {
}

console.log(parser.parse(fn));

$ node t
{ name: null,
  body: '\n',
  args: [ 'req', 'res' ],
  params: 'req, res' }

It also works if I change it to a regular async function instead of an arrow function:

$ cat t.js
const parser = require('parse-function')()

const fn = async function (req, res) {
  if (req) {}
}

console.log(parser.parse(fn));

$ node t
{ name: null,
  body: '\n  if (req) {}\n',
  args: [ 'req', 'res' ],
  params: 'req, res' }

So, strange behavior to say the least. Or maybe I'm doing something dumb. V8 at least has no problem parsing any of these versions. Thanks in advance for any support!

[tunnckoCore]

Hey there! 👋 Thanks for the report, it sounds me like problem here.
I bet it's because of this here src/index.js#L106-L113.

The idea about that if there, is if we have passed async method, then we should wrap it in object, so the parser can parse it correctly.

Can you try to add this check too and try again if it works

const isAsyncArrow = result.value.startsWith('async')

if (!(isFunction || isAsyncFn || isAsyncArrow) && isMethod) {
  result.value = `{ ${result.value} }`
}

Another reason and probably limitation is that we use babylon.parseExpression by default here, but as i remember, it was intentional.

[TooTallNate]

@charlike The patch works for me 👍 Thank you for the quick turnaround on that!

[tunnckoCore]

Sweeeet! :D I love myself sometimes for such fast responses with good end :)

PR is welcome, otherwise i can push patch in coming days. Let me know if you need some help on contributing.

[TooTallNate]

Well it's your patch. I look forward to the upcoming release 👍

[the1mills]

🐯🐯🐯🐯🐯🐯🐯🐯

[tunnckoCore]

@the1mills what? 😹 haha

@TooTallNate actually, yea, but it's not a problem for me. Go pr if you need it more soon.

[TooTallNate]

Please see #63.

@charlike P.S. I'd be happy to be added as a contributor, if this module has become a burden on your time.

[tunnckoCore]

heya, just seen your comment here.

if this module has become a burden on your time

no, it's not, just i'm in period of switching ISP providers and following through smartphone is hard, haha.

i'll add you once I get stability and time, no problem :)