Best practice for properties initialization using constructor

Question

I am declaring a "class" using a "constructor method". In both samples, properties uuid and dateCreated are initialized but in different places.

I would like to know the "best practice" in this scenario and why (also in terms of readability).

Solution A

---

define([
 'dojo/_base/declare',
 'dojo/_base/lang',
], function (declare, lang) {
 return declare('xxx.xxx.Command', null, {
 uuid: utilis.UUID(), // IS GOOD PRACTICE?
 dateCreated: Date.now(), // IS GOOD PRACTICE?
 action: null,
 properties: null
 },
 constructor: function (action, receiver, properties) {
 this.action = action;
 this.receiver = String(receiver);
 this.properties = properties;
 }
 });
});

Solution B

---

define([
 'dojo/_base/declare',
 'dojo/_base/lang',
], function (declare, lang) {
 return declare('xxx.xxx.Command', null, {
 uuid: null,
 dateCreated: null,
 action: null,
 properties: null
 },
 constructor: function (action, receiver, properties) {
 this.uuid = utilis.UUID();
 this.dateCreated = Date.now();
 this.action = action;
 this.receiver = String(receiver);
 this.properties = properties;
 }
 });
});

Answer 1

I know very little about Dojo, but for me it makes sense to keep constructor as small as possible. I wouldn't also predefine properties with null values and go with this:

define([
 'dojo/_base/declare',
 'dojo/_base/lang',
], function (declare, lang) {
 return declare('xxx.xxx.Command', null, {
 uuid: utilis.UUID(),
 dateCreated: Date.now(),
 },
 constructor: function (action, receiver, properties) {
 this.action = action;
 this.receiver = String(receiver);
 this.properties = properties;
 }
 });
});