Question

I have this string, which is generated by dojo.toJson() function:

{"page":"accommodation task=viewList","language":undefined}

When decoding it with json_decode in php it returns null.

I already figured out that this is caused by the value undefined, but I am not sure if this is to be expected or if it is a bug. Is the above string not valid json? Why can’t php just convert undefined to null?

I am using PHP 5.2.10

Answer 1

Because undefined is not valid JSON. JSON doesn’t have the JavaScript concept of undefined. It does have null, which is vaguely similar, but the usual thing (for better or worse) is to simply omit properties whose values would be undefined.

I’m surprised if Dojo’s toJson produces invalid JSON like that. You might consider using Crockford’s JSON.stringify instead. If Dojo’s toJson is really doing that, I’d report it as a bug to the Dojo team.

Update: Apparently someone did report it to them, and they closed it as invalid on the “garbage in, garbage out” theory. Not my project, but that’s just totally not how I would handle properties with undefined values… I’d omit them or throw an exception.

Update 2: As you may know, the ECMAScript 5th edition specification defines a JSON object with parse and stringify which browsers are adding support for. The specification’s definition of JSON.stringify says “undefined values are not rendered” (Section 15.12.3, Note 2) — e.g., the property should be omitted. Perhaps if you point that out to the Dojo team, they’ll rethink their GIGO response to the bug report. Also note @Felix’s comment below: They omit function references, which also can’t be validly represented in JSON, but apply a different rule to undefined.

Update 3: Still broken in Dojo 1.6.1. Here’s a live test of v1.6.0, which is the latest on the CDNs. I’ve also tested v1.6.1 and it’s still broken there too. (Not going to post a test page hotlinking to their download section, though, that would be rude.)