Should we validate method arguments in JavaScript API's?

Question

I'm developing a JavaScript library that will be used by 3rd party developers. The API includes methods with this signature:

function doSomething(arg1, arg2, options)

• arg1, arg2 are 'required' simple type arguments.
• options is a hash object containing optional arguments.

Would you recommend to validate that: - argument types are valid? - options attributes are correct? For example: that the developer didn't pass by mistake onSucces instead of onSuccess?

• why do popular libraries like prototype.js do not validate?

Answer 1

You have the right to decide whether to make a "defensive" vs. a "contractual" API. In many cases, reading the manual of a library can make it clear to it's user that he should provide arguments of this or that type that obey these and those constraints.

If you intend to make a very intuitive, user friendly, API, it would be nice to validate your arguments, at least in debug mode. However, validation costs time (and source code => space), so it may also be nice to leave it out.

It's up to you.

Answer 2

Validate as much as you can and print useful error messages which help people to track down problems quickly and easily.

Quote this validation code with some special comments (like //+++VALIDATE and //--VALIDATE) so you can easily remove it with a tool for a high-speed, compressed production version.