Parser & Compiler can't be ES6 classes

[unifiedjs]

Parser & Compiler can't be ES6 classes

[wooorm]

Hmm interesting. Wonder why classes don’t make methods enumerable.

Your code, however:

const isConstructorFunction = (value) => Boolean(value && value.prototype && value.prototype.constructor);

Will accept any function. isConstructorFunction(function () {}) // => true

[mems]

Yes right, because function(){} could be used as constructor. But () => {} couldn't.

I think the only way to do handle that is to replace:

unified/index.js

Lines 270 to 274 in 612d8dd

	if (newable(Parser)) {
	return new Parser(String(file), file).parse()
	}
	return Parser(String(file), file) // eslint-disable-line new-cap

with:

let result = null;

if (newable(Parser)) {
  // "Parser" is a class or a function (but not a generator nor an arrow function)
  result = new Parser(String(file), file)
  
  if (result.hasOwnProperty("parse")) {
    result = result.parse()
  }
} else {
  result = Parser(String(file), file)
}
 
return result

Use a simple function a constructor isn't an issue :

new function(){return ["test"]} // > Array [ "test" ]

[wooorm]

I think that works, and even simpler: the else statement isn't needed from what it seems. Could you try a PR for this?

[wooorm]

Unfortunately this will not work for compiler. Because when compiler is a normal function, it should return a string, and strings can’t be returned from a constructor.