functions-in-es6

A walk through and tests and Reflection for different kinds of functions in JavaScript till ES2015 spec.

Run tests

Using Node

npm test

Using v8

cd src
/path/to/d8 v8-d8.js

(or) if you have d8 in your $PATH,

npm run v8

How it started ?

The idea is to detect from a reference the type of function - arrow, class or a normal function. And to detect before instantiating if the reference is instantiable.

• facebook/react#4599
• http://stackoverflow.com/a/31947622/556124

This repository is about defining the function getFunctionType which returns the type of function input -

• arrow
• class
• method
• generator
• function

Definitions

Source: http://stackoverflow.com/a/31947622/556124

• arrow functions are functions that cannot be used as constructors, and don't have a .prototype property. However, methods don't either. They inherit from Function.prototype.

• classes are functions that can be called without new, and that have a .prototype object which is normally not empty. If extend was used, they don't inherit from Function.prototype.
• functions are functions that can be called either way, and do have a .prototype that is normally empty. They inherit from Function.prototype.
• generator functions are functions that do have a .prototype which inherits from the intrinsic GeneratorPrototype object, and they inherit from the intrinsic Generator object.

Implementation

getFunctionType.js

Assumptions and other gotchas

NO TRANSPILING

• Don't transpile this using babel or traceur. It will give your absolutely wrong results.

Requires ES6 features

• arrows
• generators
• classes
• enhanced object literals
• let, const
• Map
• Array.prototype.startsWith
• etc...

Function with prototypes is a class

// this will be treated as a class
function x() {}
x.prototype.a = function() {}

// this is a simple function
function y() {}

methods are detected as methods only when declared as methods

// either via enhanced object literals
let x = {
  method() {}
};

// or via class
class x {
  method() {}
}

I don't know anyway to detect the following as a method yet.

function y() {}
y.prototype.method = function() {};