Javascript extend / merge for objects.

extend.js

  /**
   * Extend an objects properties by merging with additional object arguments.
   * The source objects should be in a comma separated list after the target
   * parameter.
   * @param {object} target - The target object for the merge.
   * @return {object} The final object from target merged with additional objects in the argument list.
   */
  self._extend = function _extend(target) {
    var sources = [].slice.call(arguments, 1);
    sources.forEach(function (source) {
      for (var prop in source) {
        if (typeof source[prop] === 'object' && source[prop] !== null && !Array.isArray(source[prop])) {
          if (typeof target[prop] === 'undefined') {
            target[prop] = {};
          }
          target[prop] = self._extend(target[prop], source[prop]);
        }
        else {
          target[prop] = source[prop];
        }
      }
    });
    return target;
  };