A simple and naive extend implementation

extend.js

function extend(obj) {
  var args = [].slice.call(arguments, 1);
  args.forEach(function (source) {
    var prop;
    for (prop in source) {
      if (source.hasOwnProperty(prop)) {
        obj[prop] = source[prop]; 
      }
    }
  });
  return obj;
}

var obj = {
  a : 1
, b : 2
, c : 3
}

var ext = {
  a : 4
, b : 5
}

extend(obj, ext)
// { a: 4, b: 5, c: 3 }
obj = extend(obj, ext)
// { a: 4, b: 5, c: 3 }