json-ptr

A complete implementation of JSON Pointer (RFC 6901) for nodejs and modern browsers.

Installation

node.js

$ npm install json-ptr

Tests

Tests use mocha and expect.js, so if you clone the github repository you'll need to run:

npm install

... followed by ...

npm test

... or ...

mocha -R spec

Basics

!! This document is a work in progress even though the module is considered complete. See the examples of its use for more.

JSON Pointer provides a standardized syntax for reliably referencing data within an object's structure.

Importing

nodejs

var JsonPointer = require('json-ptr')

browser

<script src="json-ptr-0.1.0.min.js"></script>

Working with Pointers

Since most non-trivial code will make use of the same pointers over and over again (after all they represent the fixed points within a larger structure), with json-ptryou can create these pointers once and reuse them against different data items.

var manager = JsonPointer.create('/people/workplace/reporting/manager');
var director = JsonPointer.create('/people/workplace/reporting/director');

Pointers have a few simple operations:

• #get - given an origin object, returns the referenced value
• #set - given an origin object and a value, sets the referenced value

And a few useful properties:

• #pointer - an RFC 6901 formatted JSON pointer
• #uriFragmentIdentifier - an RFC 6901 formatted URI fragment identifier
• #path - an array of property names used to descend the object graph from the origin to the referenced item

Example

This example queries the live flikr api for recent images with 'surf' and 'pipeline'. It then extracts the author and the referenced media item.

Clone the repo and run it on the command line using node example/example1.js and you'll see the output. Of note: json-ptr will return undefined when any part of a pointer's path cannot be resolved, which makes this type of extraction very convenient and compact.

flikr example

var ptr = require('json-ptr')
, http = require('http')
, util = require('util')
;

var feed = "http://api.flickr.com/services/feeds/photos_public.gne?tags=surf,pipeline&tagmode=all&format=json&jsoncallback=processResponse"
/*
 * Set up some JSON pointers we'll use later...
*/
, items = ptr.create("#/items")
, author = ptr.create("#/author")
, media = ptr.create("#/media/m")
;

function extractItems(it) {
	return items.get(it);
}

function extractAuthorAndMedia(it, i) {
	this.push({
		author: author.get(it),
		media : media.get(it)
	});
}

function processResponse(json) {
	var items = extractItems(json)
	, accum = []
	;

	if (items && Array.isArray(items)) {
		items.forEach(extractAuthorAndMedia, accum);
	}

	console.log( util.inspect(accum, true, 99) );
}

http.get(feed, function(res) {
	console.log("Got response: " + res.statusCode);

	var data = '';

	res.on('data', function (chunk){
		data += chunk;
	});

	res.on('end',function(){
		// result is formatted as jsonp... this is for illustration only.
		eval(data);
	})
}).on('error', function(e) {
	console.log("Got error: " + e.message);
});