debut JSON

I've checked in some JSON functionality, specifically a lightly modified version of Crockford's json2.js. Crockford's code had global effects, and I dislike that, so I made some changes. The parse and stringify functions appear within extensions.org.icongarden.json (big surprise). As well, the extension doesn't modify the prototype of Date, which means stringify doesn't convert instances of Date, which isn't part of JSON anyway. If I end up doing anything special with Date, it won't involve altering any prototype.

There was a discussion on the V8 list recently about JSON performance, with various folk making all kinds of claims unsupported by data, so I thought I'd generate some. Note this is the farthest thing from scientific or comprehensive, but it's a start. I wrote a test script with collects a hierarchy of objects describing some sub-directories on my disk, converts it to JSON, and finally converts it back to the hierarchy it started with. Each object contains a couple of strings and a number in addition to zero or more child nodes. Here's the output of my test script:

• milliseconds to enumerate: 203
• milliseconds to stringify: 2053
• milliseconds to parse: 1060

Surprisingly, the enumerate operation is by far the fastest. It's surprising because enumerating the sub-directories involves several hundred system calls, whereas I presume the stringify and parse operations involve none (aside, perhaps, from the occasional brk). Worse, at least some of these system calls touch the disk.

Let's ignore the stringify time for a moment and focus on the parse time. It's over five times the enumerate time, which is surprising enough, but when you consider how parse works, it's even more surprising. This function is basically a validating front end for eval involving a regular expression, which makes me wonder if V8's eval or regular expression engine could be a lot faster.

Finally, let's ponder stringify. It's all JavaScript, so it makes sense that it's slower than parse, but an order of magnitude slower than the enumerate operation? That seems crazy.

I'm going to leave things the way they are now because the important thing is to establish an interface for these functions so I can build other things atop it, but I have a feeling I'll be coming back to this.

Update: I renamed parse and stringify as decode and encode, respectively. Now I can refer to the JSON extension as a "codec" and stick out my chest in some kind of geek macho display.