Mixins in Javascript

extend.js

function extend() {
  var destination = arguments[0];
  for (var i = 1; i < arguments.length; i++) {
    var source = arguments[i];

    for (var k in source) {
      if (source.hasOwnProperty(k)) {
        destination[k] = source[k];
      }
    }
  }
  return destination; 
}