Parse bound functions

[mauriciomelo]

reproduce:

const parser = require('parse-function')();

const foo = function foo() { return this.message; };
parser.parse(foo.bind({ message: 'hello' }))

error:

SyntaxError: Unexpected token, expected , (1:22)
      at Parser.raise (node_modules/parse-function/node_modules/babylon/lib/index.js:807:15)
      at Parser.unexpected (node_modules/parse-function/node_modules/babylon/lib/index.js:2108:16)
      at Parser.expect (node_modules/parse-function/node_modules/babylon/lib/index.js:2094:28)
      at Parser.parseExprList (node_modules/parse-function/node_modules/babylon/lib/index.js:3884:14)
      at Parser.parseExprAtom (node_modules/parse-function/node_modules/babylon/lib/index.js:3185:30)
      at Parser.parseExprSubscripts (node_modules/parse-function/node_modules/babylon/lib/index.js:2864:21)
      at Parser.parseMaybeUnary (node_modules/parse-function/node_modules/babylon/lib/index.js:2842:21)
      at Parser.parseExprOps (node_modules/parse-function/node_modules/babylon/lib/index.js:2751:21)
      at Parser.parseMaybeConditional (node_modules/parse-function/node_modules/babylon/lib/index.js:2721:21)
      at Parser.parseMaybeAssign (node_modules/parse-function/node_modules/babylon/lib/index.js:2680:21)
      at Parser.parseExpression (node_modules/parse-function/node_modules/babylon/lib/index.js:2634:21)
      at Parser.parseStatementContent (node_modules/parse-function/node_modules/babylon/lib/index.js:4157:21)
      at Parser.parseStatement (node_modules/parse-function/node_modules/babylon/lib/index.js:4045:17)
      at Parser.parseBlockOrModuleBlockBody (node_modules/parse-function/node_modules/babylon/lib/index.js:4590:23)
      at Parser.parseBlockBody (node_modules/parse-function/node_modules/babylon/lib/index.js:4576:10)
      at Parser.parseBlock (node_modules/parse-function/node_modules/babylon/lib/index.js:4565:10)
      at Parser.parseFunctionBody (node_modules/parse-function/node_modules/babylon/lib/index.js:3814:24)
      at Parser.parseFunctionBodyAndFinish (node_modules/parse-function/node_modules/babylon/lib/index.js:3792:10)
      at Parser.parseFunction (node_modules/parse-function/node_modules/babylon/lib/index.js:4717:10)
      at Parser.parseFunctionExpression (node_modules/parse-function/node_modules/babylon/lib/index.js:3259:17)
      at Parser.parseExprAtom (node_modules/parse-function/node_modules/babylon/lib/index.js:3193:21)
      at Parser.parseExprSubscripts (node_modules/parse-function/node_modules/babylon/lib/index.js:2864:21)
      at Parser.parseMaybeUnary (node_modules/parse-function/node_modules/babylon/lib/index.js:2842:21)
      at Parser.parseExprOps (node_modules/parse-function/node_modules/babylon/lib/index.js:2751:21)
      at Parser.parseMaybeConditional (node_modules/parse-function/node_modules/babylon/lib/index.js:2721:21)
      at Parser.parseMaybeAssign (node_modules/parse-function/node_modules/babylon/lib/index.js:2680:21)
      at Parser.parseExpression (node_modules/parse-function/node_modules/babylon/lib/index.js:2634:21)
      at Parser.getExpression (node_modules/parse-function/node_modules/babylon/lib/index.js:2609:21)
      at Object.parseExpression (node_modules/parse-function/node_modules/babylon/lib/index.js:10203:17)
      at Object.getNode (node_modules/parse-function/dest/index.js:91:18)
      at Object.parse (node_modules/parse-function/dest/index.js:367:24)
      at Context.it.only (lib/rodar.spec.js:27:14)

[tunnckoCore]

bind is not preferred, this - too. I understand that there are cases such in react, but I dont think it is a problem here - the parser fail so I cant do much (looking in first glance).

that's the beauty of the plugins api, try handle it with plugin?

[tunnckoCore]

with "this" above I mean this

[mauriciomelo]

The example above is the simplest I could reproduce, the real scenario is bit more complex, I want to be able to parse a class (instance) method and preserve it's context. I don't have much control over what is passed to my lib's public api, that's why I can't refact it to not use this.

The interesting part is that when I use babylon.parse() directly it does not throw any error.

[tunnckoCore]

because we use parseExpression by default.

why not just pass that method instead of passing bound fn of it?

[mauriciomelo]

why not just pass that method instead of passing bound fn of it?

passing just the method seems to not preserve the context

But... I was wondering that even if the bound fn did parse I would lose the params (and defaults) because:

> ((a = 42) => {}).toString()
 "(a = 42) => {}"

but

> ((a = 42) => {}).bind().toString()
"function () { [native code] }"

My options right now are:

• pass the entire instance (not only the method), for example myLib.define(instance) instead of myLib.define(instance.method)
• add an optional param to handle context, for example myLib.define(instance.method, { context: instance })

Anyway, thank you for your support and quick reply

[tunnckoCore]

What context, what five dollars? Sorry, but absolutely seriously, I can't get for what you are talking about. ;/

You just pass a function and then work with its parsed parts - params, name and string body. Nothing to deal with context, we do nothing to your function too, its context is the same.

What are you trying to do? Can u share code?

[mauriciomelo]

the problem is that my lib didn't accept plain objects, so I had to pass an array of functions. the process of converting object methods into an array makes it "unbind" it's parent, for example

const { parse } = require('parse-function')();

class Foo {
    constructor() {
        this.bar = 42;
    }

    hello() {
        return this.bar;
    }
}

const foo = new Foo();
const hello = foo.hello; // unpacking makes it forget the parent context

myLibPublicFunction([hello])

function myLibPublicFunction (definitions) { 
    const fn = definitions[0];
    parse(fn) // ok

    // but I have to do some other stuff with fn
    fn() // ops, no context
}

// because of that I had to bind
myLibPublicFunction([hello.bind(foo)]);
// it makes fn() happy but not parse(fn)

// so I simplified everything by making my public api accept an object instead of an array
myLibPublicFunction(foo);
function myLibPublicFunction (instance) { 
    parse(instance.hello) // happy
    instance.hello() // happy
}

there are probably a bunch of typos there but hopefully it is understandable

[tunnckoCore]

oh yea, I got it. it was definitely an architecture/concept design mistake. so yea, always thinking twice is the best thing