Thanks for the report.

$.param expects an object which undefined is not so passing undefined is unsupported. I'll treat it as a feature request then and leave open for now so that others can voice their opinions.

We've recently made $.map & $.each accept undefined/null input so I'm not opposed to treating them lightly here. We should determine, though, how many more methods would have to get similar treatment.

Thanks, yeah I figured it's more of a "nice to have" feature, just wanted to get it out there just incase no one ran into it!

This is really easy to fix on the caller's side though. If you know the value may be undefined, use the || "" trick to define it as an empty string. If we put a bunch of this inside jQuery itself, there is a good chance it will mask errors and make the API harder for people to use.

@dmethvin You could say the same about $.map/$.each, though and yet we accepted to treat null & undefined differently.

I agree. If those weren't regressions (in undocumented behavior) I don't think we would have changed them. Or at least I wouldn't have been in favor of it. 😄

I'd tend to think consistency trumps history in the matter and I'd be in favor of gracefully handling the nul/undefined case.

So is the suggestion to handle just $.param(undefined) here, or are we creating a bigger ticket to review all the APIs and allow null/undefined where possible? Will we update all the docs as well? The APIs have been around for almost a decade without someone needing this so I'm concerned we're moving into yak-shaving territory with so much else we have to do.

Should we treat it as a breaking change or a new feature? In the latter case this could be moved to 3.1.0; I'd rather not add new issues to the 3.0.0 milestone at this point.

Definitely a feature, since we're talking about expanding the signature.

OK, milestone 3.1.0 added.

(Hopefully not too far off topic) Since a change is being considered to handle null and undefined, would it be a bad idea to also handle a function argument? Similar to how object iterator invokes attributes that are functions.

$.param(function(){
  var params = {};
  // Build params
  return params;
});

I'm not a fan of adding more behavior to this API (and documenting it, don't forget). Unfortunately I suppose we've already crossed the Rubicon by calling functions at all, which prevent $.param() from being used as a way to passively serialize an object the way you would with JSON. But I'm still not a fan!

@dmethvin I moved this question to separate issue.