Helper function for extending objects

extend.js

/**
   * Check if object is part of the DOM
   * @constructor
   * @param {Object} obj element to check
   */
  function isDOMElement(obj) {
    return obj && typeof window !== 'undefined' && (obj === window || obj.nodeType);
  }
  
/**
   * Helper function for extending objects
   */
  function extend (object /*, objectN ... */) {
    if(arguments.length <= 0) {
      throw new Error('Missing arguments in extend function');
    }
  
    var result = object || {},
        key,
        i;
  
    for (i = 1; i < arguments.length; i++) {
      var replacement = arguments[i] || {};
  
      for (key in replacement) {
        // Recurse into object except if the object is a DOM element
        if(typeof result[key] === 'object' && ! isDOMElement(result[key])) {
          result[key] = extend(result[key], replacement[key]);
        }
        else {
          result[key] = result[key] || replacement[key];
        }
      }
    }
  
    return result;
  }