extend.js

// Grab from jQuery.extend()
// https://github.com/jquery/jquery/blob/master/src/core.js

function extend() {
  var options, name, src, copy, clone,
    target = arguments[0] || {},
    i = 1,
    length = arguments.length,
    deep = false;

  // Handle a deep copy situation
  if (target.constructor == Boolean) {
    deep = target;
    target = arguments[1] || {};
    // skip the boolean and the target
    i = 2;
  }

  for (; i < length; i++) {
    // Only deal with non-null/undefined values
    if ((options = arguments[i]) != null) {
      // Extend the base object
      for (name in options) {
        src = target[name];
        copy = options[name];

        // Prevent never-ending loop
        if (target === copy) {
          continue;
        }

        // Recurse if we're merging plain objects or arrays
        if (deep && copy && (copy.constructor == Object || copy.constructor == Array)) {
          clone = src && src.constructor == copy.constructor ? src : new copy.constructor();
          // Never move original objects, clone them
          target[name] = extend(deep, clone, copy);

        // Don't bring in undefined values
        } else if (copy !== undefined) {
          target[name] = copy;
        }
      }
    }
  }

  // Return the modified object
  return target;
}

// CommonJS
if (typeof module != 'undefined' && module.exports) {
  module.exports = extend;
}