js cloning

clone.js

// inspired by https://github.com/bestiejs/lodash/blob/master/lodash.js
// but supports cloning custom constructor instances
// still need to implement Date, RegExp

//If Object.create isn't already defined, we just do the simple shim, without the second argument,
//since that's all we need here
var Object_create = Object.create;
if (typeof Object_create !== 'function') {
    Object_create = function(o) {
        function F() {}
        F.prototype = o;
        return new F();
    };
}

var arrayClass = '[object Array]';
function isArray (value) {
	return toString.call(value) == arrayClass;
}

function clone(source, deep, sourceStack, cloneStack) {
	// immediately return source with value semantics
    if (source == null || typeof(source) !== 'object') {
        return source;
    }
    // default to shallow
    deep || (deep = false);
    
    var isArr = isArray(source);
    
	//make sure the returned object has the same type and prototype as the original
    var cloned = isArr ? [] : Object_create(source.constructor.prototype);
    
    if ( deep ) {
		sourceStack || (sourceStack = []);
		cloneStack || (cloneStack = []);
		
		// check for circular references and return corresponding clone
		var length = sourceStack.length;
		while ( length-- ) {
		  if ( sourceStack[length] == source ) {
		    return cloneStack[length];
		  }
		}
		
		// add the source value to the stack of traversed objects
		// and associate it with its clone
		sourceStack.push(source);
		cloneStack.push(cloned);
    }
    
    if ( isArr ) {
    	var length = source.length;
    	while ( length-- ) {
			cloned[length] = deep ? clone( source[length], deep, sourceStack, cloneStack ) : source[length];
		}
    }
    else {
		for ( var key in source ) {
			if ( ! source.hasOwnProperty(key) ) continue;
			cloned[key] = deep ? clone( source[key], deep, sourceStack, cloneStack ) : source[key];
		}
    }
    
    return cloned;
}

module.exports = clone