i-json

Fast incremental JSON parser

i-json is a fast incremental JSON parser implemented in C++.

See https://github.com/joyent/node/issues/7543#issuecomment-43974821 for background discussion.

The focus of i-json is on performance. The API is minimal and designed for speed but i-json can be used as a fast engine to power higher level JSON APIs (evented, streaming).

Installation

npm install i-json

API

var ijson = require('i-json');
 
var parser = ijson.createParser();
 
// update the parser with the next piece of JSON buffer.
// This call will typically be issued from a 'data' event handler
parser.update(jsonChunk);
 
// retrieve the result
var obj = parser.result();

You can pass a Buffer or a string to parser.update. If you get your input data in a Buffer, you should pass it directly to parser.update; you should not convert it and pass it as a string.

You can also configure a callback which will be called during parsing:

var parser = ijson.createParser(callback, maxDepth);

function callback(value, path) {
    // ...
    return value;
}

callback receives the value and the path to the value. path is an array of object keys and array indexes that lead to the value.

The callback also allows you transform the value. If you return undefined from the callback, the parsed value will not be recorded into the final result. So you can implement a high level evented API by emitting events from the callback and returning undefined.

maxDepth lets you control the granularity of the callbacks. The callback will only be called when the depth of parsing is <= maxDepth. If you omit maxDepth the callback will be called on all the values.

Example

var ijson = require('i-json');
 
var parser = ijson.createParser(function(value, path) {
    console.log(path.length + ": " + path.join('/') + ": " + JSON.stringify(value));
    return value;
}, 2);
 
parser.update(new Buffer('{"data": [2, 3, [true, false]], "message": "hello" }'));
console.log("result=" + JSON.stringify(parser.result()));

Output:

2: data/0: 2
2: data/1: 3
2: data/2: [true,false]
1: data: [2,3,[true,false]]
1: message: "hello"
0: : {"data":[2,3,[true,false]],"message":"hello"}
result={"data":[2,3,[true,false]],"message":"hello"}

Note that the true and false values are not output individually, but they will if we increase or omit maxDepth.

Performance

Typical results of the test program (parsing an 8 MB file 10 times) on my MBP i7

JSON.parse: 632 ms
I-JSON single chunk: 1046 ms
I-JSON multiple chunks: 1278 ms

License

MIT license.