es6-altEgo

Give your constructors and alter ego, allowing classes to be used as both a constructor() and a function().

Tiny, <20 lines of code
Fast - practically no impact on performance
Requires an ES6 environment with new.target.
Won't work in IE, works great in all other browsers

Why?

So, I ran in to that issue where you can't invoke a constructor() as a normal function, it can only be used with new.

After doing some refactoring, I realised I'd have to rewrite a bunch of documentation. That's where I snapped...

The problem

class foo {
  constructor() {
    console.log( 'hello from ego foo!' );
  }
}

foo(); // Class constructor foo cannot be invoked without 'new'

Why would you ever want to do this?

Well, maybe you want to dual-purpose your class to work both as a constructor new foo() or as a mixin foo( someObj ).

The solution

import altEgo from './path-to/altEgo.js';

class foo {
  // ...
}

const alt = function( ...args ) {
  console.log( 'hello from alt foo!' );
}

foo = altEgo( alt, foo ); // the new foo is pretty much identical twin of the original foo

foo(); // hello from alt foo!

void new foo(); // hello from ego foo!

class bar extends foo {
  constructor() {
    console.log( 'hello from ego bar!' );
    super();
  }
}

void new bar(); // hello from ego bar!
                // hello from ego foo!

bar(); // Class constructor bar cannot be invoked without 'new'
       // ...because we didn't altEgo() `bar`

Alt extras

The alternate function gets two properties:

ego - the constructor (in our case, the original foo)
mask - the mask function (in our case, the new foo)

For example, you could do:

const alt = function( ...args ) {
  return new alt.ego( ...args );
}

In which case invoking let ifoo = foo( some, args ) would give same results as let ifoo = new foo( some, args ).

Credits

Based on a idea by Bergi.

License

"The Unlicense", ie. public domain. Because screw lawyers.

originalfoo / es6-altEgo