js-extend/extend.js

A simple extend function based on underscore

(function(factory) {
  if(typeof exports === 'object') {
    factory(exports);
  } else {
    factory(this);
  }
}).call(this, function(root) { 

  var slice   = Array.prototype.slice,
      each    = Array.prototype.forEach;

  var extend = function(obj) {
    if(typeof obj !== 'object') throw obj + ' is not an object' ;

    var sources = slice.call(arguments, 1); 

    each.call(sources, function(source) {
      if(source) {
        for(var prop in source) {
          if(typeof source[prop] === 'object' && obj[prop]) {
            extend.call(obj, obj[prop], source[prop]);
          } else {
            obj[prop] = source[prop];
          }
        } 
      }
    });

    return obj;
  }

  root.extend = extend;
});