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;
        }
    });
});