Question

Are there any performance or functional differences between having a javascript constructor return a JavaScript object literal, versus simply setting properties with this.XYZ. For example:

    function PersonA(fname, lname) {
        this.fname = fname;
        this.lname = lname;
    }

    function PersonB(fname, lname) {
        return {
            "fname": fname,
            "lname": lname
        };
    }

Both seem to behave appropriately:

    PersonA.prototype.fullName = function() { return this.fname + " " + this.lname; };
    PersonB.prototype.fullName = function() { return this.fname + " " + this.lname; };

    var pA = new PersonA("Bob", "Smith");
    var pB = new PersonB("James", "Smith");

    alert(pA.fullName());
    alert(pB.fullName());

Is one preferable for any reason, or is it a matter of taste? If taste, is one more standard?

Answer 1

They’re not entirely identical.

If you return the object being created from the constructor…

• it will inherit from the prototype of the constructor
• it will have instanceof available as a means of testing which constructor created it

The reason the fullName() method seems to work for pB is that you’re using the PersonA constructor for both.

var pA = new PersonA("Bob", "Smith");   // uses PersonA constructor
var pB = new PersonA("James", "Smith"); // uses PersonA constructor???

FYI, the proper term is “JavaScript object literal”, not “JSON object literal”.

---

EDIT: You’ve updated the code in the question to use the PersonB constructor. Run it again, and you’ll find an Error in the console.