I don't think an Express view engine belongs into this module. As it is common in the JavaScript ecosystem, you could create a express-pithy module and join others.

Also, require is synchronous and therefore hurts Node.js in its asynchronous nature.

require is auto-cachable, and all other view engines do the same: first time view render request recieved, it prepared by view engine and cached somethere. Of course you can pre-cache all views at application startup as you shown in your examples, but that should be done per project and described in README.md.

express-pithy will require to maintain project which I do not want to do.

I saw another flaws in pithy:

• It is allowed to specify multiple ids per tag html.div('#id1#id2'), but this should be disallowed as it is disallowed in HTML spec.
• It does not supports branching and loops. I need html.div(null, [function() { if (something) { return html.div(null, 'bla-bla-bla'); } else { return html.div(null, 'yadda-yadda-yadda'); }]).
• Small optimizations can be done like removing useless function attrPairs().

So perhaps I will create my own library, but not open-source.

I'm currently reading blog of @caolan , it is very cool.

require is auto-cachable, and all other view engines do the same: first time view render request recieved, it prepared by view engine and cached somethere.

But the template files are being loaded asynchronously. require loads synchronously.

• It is allowed to specify multiple ids per tag html.div('#id1#id2'), but this should be disallowed as it is disallowed in HTML spec.

You're right. The question is if this should be enforced by pithy.

• It does not supports branching and loops. I need html.div(null, [function() { if (something) { return html.div(null, 'bla-bla-bla'); } else { return html.div(null, 'yadda-yadda-yadda'); }]).

What about this?

html.div(null, [
    something
        ? html.div(null, 'bla-bla-bla')
        : html.div(null, 'yadda-yadda-yadda')
])

So perhaps I will create my own library, but not open-source.

Why not? It may help other people.