strict.js

var strict = function (fn) {
  'use strict';

  var args;

  var STRIP_COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg;
  var ARG_NAMES = /([^\s,]+)/g;
  
  var fnStr = fn.toString().replace(STRIP_COMMENTS, '');
  args = fnStr.slice(fnStr.indexOf('(')+1, fnStr.indexOf(')')).match(ARG_NAMES);
  if (args === null) {
    args = [];
  }

  var getGlobals = function (obj, args) {
    var globals = [];
    args.forEach(function (arg) {
      globals.push(obj[arg]);
    });
    
    fn.apply(obj, globals);
  };

  if (typeof window !== 'undefined') {
    getGlobals(window, args);
  } else if (typeof global !== 'undefined') {
    getGlobals(global, args);
  } else {
    throw "Can't find window/global object. Are you doing something weird?";
  }
};

strict(function ($) {
  console.log(typeof $); // read-only global
  $ = null;
  console.log(typeof $); 
  console.log(typeof this.$); // read/write global
});