array-like NodeList via mixins

nodeListMixin.js

var NodeList = function() {};
var nodeListExtras = {x: 23};
mixin(NodeList.prototype, Array.prototype, nodeListExtras);

function mixin(obj /*, mixins*/) {
  var mixins = [].slice.call(arguments, 1);
  for (var i=0; i<mixins.length; i++) {
    var thisMixin = mixins[i];
    var props = Object.getOwnPropertyNames(thisMixin);
    for (var j=0; j<props.length; j++) {
      obj[props[j]] = thisMixin[props[j]];
    }
  }
  return obj;
}

var nodeList = new NodeList();

console.log(nodeList instanceof NodeList); //true
console.log(nodeList instanceof Array); //false
console.log(nodeList.push); //native function
console.log(nodeList.x); //23