This looks like a combination of JSONP and the ES2015 computed property name syntax. JSONP is used to load into web pages using a script tag and execute the function (item) with the data, rather than a direct response from Ajax.
As for tools, jq may be able to parse this assuming you remove the item( and the last );
It's similar, but JavaScript would use : and , for separators rather than = and ;.
This is valid Lua table syntax, however. A program creates an embedded Lua environment with an item callback function and runs this file inside it. Something similar could be done to convert it to another format; just define item to output the data as JSON, or whatever other format you prefer.
The Prosody XMPP server, written in Lua, generates files of this type when serializing lists with the "internal" storage manager. See functions list_store and list_load in util/datamanager.lua.
So, it might be some JSON meta language. I just find it weird that it seems to contain all data, so you wouldn't use this for validating or templating JSON.
But ultimately, it also means with a handful of regex replacements, you could turn this particular file into JSON. Might make building your own parser almost trivial...
I'm going to have to go a step deeper and find out what's going on in the code because this section is repeated many many times. It's not just this one that I need to parse.
.. It might even be easier to write my own parser like you said, because I need to take actions based on the date fields.