Force function as constructor

README.md

140byt.es::forcetor

A 116 byte tweet-sized snippet of code you can paste into ANY constructor function without modification to force use as a constructor.

How to use

Use the constructor with or without new, and receive back an instance object.

OR...

Copy and paste the following code into the top of your constructor (116 chars):

var a=arguments,b=a[0],c=a.callee;if(!(this instanceof c))return new c(a);if(c==b.callee)return c.apply(this,b);

annotated.js

// This function is intended to be used ONLY as a constructor.
function(
  x, // Some variables to pass to the constructor
  y  // and set on the instance object
){
  // BEGIN PASTABLE FORCETOR CODE
  var a=arguments,         // minification
    b=a[0],                // first argument, can't use x
                           // would break no modification paste
    c=a.callee,            // the constructor
    d=this;                // only used for the 140 bytes example

  if(!(d instanceof c))    // check if "new" was used
    return new c(a);       // force "new" w/arguments as first argument

  if(c==b.callee)          // if first argument is an arguments object
                           // that originated from this constructor
    return c.apply(d,b);   // call constructor w/new instance and proper arguments
  // END PASTABLE FORCETOR CODE


  // YOUR CONSTRUCTOR CODE HERE
  d.x=x;                   // set values on this with confidence
  d.y=y;                   // knowing with certainty you're in a constructor
}

example.js

var A = function(x,y){var a=arguments,b=a[0],c=a.callee,d=this;if(!(d instanceof c))return new c(a);if(c==b.callee)return c.apply(d,b);d.x=x;d.y=y;};

var a = A(1,2);
console.log(a.x, a.y);        // 1 2
console.log(a instanceof A);  // true

var b = new A(3,4);
console.log(b.x,b.y);         // 3 4
console.log(b instanceof A);  // true

index.js

function(x,y){var a=arguments,b=a[0],c=a.callee,d=this;if(!(d instanceof c))return new c(a);if(c==b.callee)return c.apply(d,b);d.x=x;d.y=y;}

LICENSE.txt

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
                    Version 2, December 2004

 Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE>

 Everyone is permitted to copy and distribute verbatim or modified
 copies of this license document, and changing it is allowed as long
 as the name is changed.

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. You just DO WHAT THE FUCK YOU WANT TO.

package.json

{ "name": "forcetor",
  "description": "Force function use only as a constructor",
  "keywords": [
    "140bytes",
    "constructor",
    "ctor",
    "forcetor"
  ]
}