[ashkankiani]

You are a bad programmer if you think silently doing the wrong thing is not a bug. The right thing to do with unexpected input as the setTimeout library author is to raise an exception.

[balls187]

The wrong thing, or the undefined thing?

Feel free to make a proposal to ECMA.

[log_e]

It's in the standard library. You're a bad programmer if you don't learn the ins and outs of the standard library, or make sweeping generalizations.

[notpushkin]

Standard library is an API just like any other library. The only thing different about it is backward compatibility (which in JS is paramount and the is reason setTimeout can't be fixed directly). It is a bad design still.