Object.setPrototypeOf(O, proto) full/complete polyfill with boolean flag for partial implementation.

Object.setPrototypeOf.js

/*jslint devel: true, indent: 2 */
// 15.2.3.2
if (!Object.setPrototypeOf) {
  Object.setPrototypeOf = (function(Object, magic) {
    'use strict';
    var set;
    function checkArgs(O, proto) {
      if (typeof O !== 'object' || O === null) {
        throw new TypeError('can not set prototype on a non-object');
      }
      if (typeof proto !== 'object' && proto !== null) {
        throw new TypeError('can only set prototype to an object or null');
      }
    }
    function setPrototypeOf(O, proto) {
      checkArgs(O, proto);
      set.call(O, proto);
      return O;
    }
    try {
      // this works already in Firefox and Safari
      set = Object.getOwnPropertyDescriptor(Object.prototype, magic).set;
      set.call({}, null);
    } catch (o_O) {
      if (
        // IE < 11 cannot be shimmed
        Object.prototype !== {}[magic] ||
        // neither can any browser that actually
        // implemented __proto__ correctly
        // (all but old V8 will return here)
        {__proto__:null}.__proto__ === void 0
        // this case means null objects cannot be passed
        // through setPrototypeOf in a reliable way
        // which means here a **Sham** is needed instead
      ) {
        return;
      }
      // nodejs 0.8 and 0.10 are (buggy and..) fine here
      // probably Chrome or some old Mobile stock browser
      set = function(proto) {
        this[magic] = proto;
      };
      // please note that this will **not** work
      // in those browsers that do not inherit
      // __proto__ by mistake from Object.prototype
      // in these cases we should probably throw an error
      // or at least be informed about the issue
      setPrototypeOf.polyfill = setPrototypeOf(
        setPrototypeOf({}, null),
        Object.prototype
      ) instanceof Object;
      // setPrototypeOf.polyfill === true means it works as meant
      // setPrototypeOf.polyfill === false means it's not 100% reliable
      // setPrototypeOf.polyfill === undefined
      // or
      // setPrototypeOf.polyfill ==  null means it's not a polyfill
      // which means it works as expected
      // we can even delete Object.prototype.__proto__;
    }
    return setPrototypeOf;
  }(Object, '__proto__'));
}

This doesn't work on Opera 12 -- setPrototypeOf.polyfill = true, but Object.setPrototypeOf(foo, null) doesn't work.

Hacky workaround in paulmillr/es6-shim#223

Thanks for your code!

Can you let me know which license is used for distribution of this code?
I'd like to use this code for a commercial app so I need to check the license.

Happy coding! :)