Question

Is there a performance advantage in using an object literal over a self instantiated constructor?

Examples

Object literal:

var foo = { 
    //... 
};

Self instantiated constructor:

var foo = new function () {
    //...
};

Question

Is there a performance advantage in using an object literal over a self instantiated constructor?

Examples

Object literal:

var foo = { 
    //... 
};

Self instantiated constructor:

var foo = new function () {
    //...
};

• javascript
• performance
• object

• 2 see jsperf./object-notation-vs-constructor – Arun P Johny Commented Aug 13, 2013 at 1:01
• Modified perf (see rev. 5) did not expect Object.create to be so slow! – Paul S. Commented Aug 13, 2013 at 10:39

1 Answer 1

Yes (the object literal will be faster), but they are subtly different in implementation¹ and represent different goals. The constructor form "has to do a bunch more stuff" while the literal form can also be more highly optimized - it is a definition (of an as-of-yet-fixed set of properties), and not a sequence of statements.

Even though a micro-benchmark (which is interesting, thanks Arun!) might show one being "much slower", it Just Doesn't Matter in a real program² as the amount of relative time spent in either construct approaches nothing.

¹ When a constructor is used a prototype must be introduced. This is not the case with an object literal due to it's fixed chain behavior.

Every object created by a constructor has an implicit reference (called the object’s prototype) to the value of its constructor’s “prototype” property.

Other overhead work includes creating a new execution context, copying over additional properties, and even checking the return value. (In the posted case it also has to create a new one-off function object before it can even use is as a constructor which itself adds some additional overhead).

² I'm sure there are counter-examples. But for such cases, I can only hope that the problem has been thoroughly benchmarked with all other bottlenecks identified and removed.