classical.js

var Proto = function (thing) {
  this.thing = thing;
};

Proto.prototype.method = function () {
  return this.thing;
};

Proto.prototype.prop = 42;

var p = new Proto("someThing");
p.method(); // "someThing"

Proto.js

var Proto = {
  prop: 42,
  method: function () {
    return this.thing;
  },
  constructor: function (thing) {
    this.thing = thing;
  }
};

// instantiate
var p = Object.create(Proto);
// initialize
p.constructor("someThing");
// call method
p.method(); // "someThing"