the worst idea imaginable

expect-type.js

(function () {

  'use strict';

  var slice = Array.prototype.slice;


  Function.prototype.expect = function expect () {
    var argTypes = slice.call(arguments);
    var functionToCall = this;

    return function expectWrap () {
      var args = slice.call(arguments);

      for (var i = 0, l = argTypes.length; i !== l; i++) {
        if (args[i].constructor !== argTypes[i]) {
          throw new TypeError('Expected ' + argTypes[i].name + ' for ' + suffix(i) + ' argument');
        }
      }

      return functionToCall.apply(this, args);
    };
  };


  function suffix (number) {
    return {
      '1': '1st',
      '2': '2nd',
      '3': '3rd'
    }[++number] || number + 'th';
  }

}());