A deep copier for JavaScript

deepCopy.js

/*
  A deep copier for JavaScript
  that can handle circular references,
  copies objects with correct prototypes,
  copies functions (rather than referencing them),
  copies non-enumerable properties
  and copies HTML- and jQuery-elements as references
*/

function deepCopy(obj){
  
  // Memory handling circular references
  var mem = [], mem2 = [];
  function remem(obj,newObj){
    if(!newObj){
      return mem2[mem.indexOf(obj)];
    }
    mem.push(obj);
    mem2.push(newObj);
  }

  function clone(obj){
    var newObj;

    // Primitives and stuff we want to copy by reference (DOM els etc)
    var primitives = [String,Number,Boolean];
    typeof HTMLElement != "undefined" && primitives.push(HTMLElement);
    typeof HTMLCollection != "undefined" && primitives.push(HTMLCollection);
    typeof jQuery != "undefined" && primitives.push(jQuery);
    
    // Find out if this is a "primitive"
    var primitive = primitives.some(function(x){
      if(obj===null || obj===undefined){return true;}
      return obj === x ||
        obj.constructor === x ||
        obj instanceof x ||
        // old IE:s don't have HTMLElement
        (typeof HTMLElement == "undefined" && obj.nodeType);
    });

    // Primitive 
    if(primitive){
      newObj = obj;
    }
    // Circular reference
    else if(remem(obj)){
      return remem(obj);
    }
    // Function
    else if(obj instanceof Function){
      eval("newObj = " + obj);
    }
    // Array
    else if(obj instanceof Array){
      newObj = [];
    }
    // Object
    else {
      try {
        newObj = Object.create(obj.__proto__);
      }
      catch(e){
        newObj = {};
      }
    }

    if(!primitive){
      // Write to the memory handling circular references
      remem(obj,newObj);

      // Recurse / copy properties of non-primitives
      if(Object.getOwnPropertyNames){
        // copy non iteratable props as well
        Object.getOwnPropertyNames(obj).forEach(function(i){
          newObj[i] = clone (obj[i]);
        });
      }
      else {
        // old browsers
        for(var i in obj){
          if(!obj.hasOwnProperty(i)){continue;}
          newObj[i] = clone(obj[i]);
        }
      }
    }

    return newObj;
  }

  return clone(obj);
}