Json-ptr NPM | npm.io

json-ptr

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

Background

I wrote this module a couple of years ago when I was unable to find what I considered a complete implementation of RFC 6901. It turns out that I now use the hell out of it.

Since there are a few npm modules for you to choose from, see the section on performance later in this readme; you can use your own judgement as to which package you should employ.

Install

npm install json-ptr

Use

nodejs

import { JsonPointer, create } from 'json-ptr';

Module API

Classes

JsonPointer : class – a convenience class for working with JSON pointers.
JsonReference : class – a convenience class for working with JSON references.

Functions

All example code assumes data has this structure:

const data = {
  legumes: [{
    name: 'pinto beans',
    unit: 'lbs',
    instock: 4
  }, {
    name: 'lima beans',
    unit: 'lbs',
    instock: 21
  }, {
    name: 'black eyed peas',
    unit: 'lbs',
    instock: 13
  }, {
    name: 'plit peas',
    unit: 'lbs',
    instock: 8
  }]
}

.create(pointer: string | string[]): JsonPointer

Creates an instance of the JsonPointer class.

arguments:

pointer : string, required – a JSON pointer in JSON string representation or URI fragment identifier representation

returns:

a new JsonPointer instance

example:

const pointer = JsonPointer.create('/legumes/0');
// fragmentId: #/legumes/0

.has<T>(target: T, pointer: string | string[] | JsonPointer): boolean

Determins whether the specified target has a value at the pointer's path.

arguments:

target : object, required – the target object
pointer : string, required – a JSON pointer in JSON string representation or URI fragment identifier representation

returns:

the dereferenced value or undefined if nonexistent

.get(target,pointer)

Gets a value from the specified target object at the pointer's path

arguments:

target : object, required – the target object
pointer : string, required – a JSON pointer in JSON string representation or URI fragment identifier representation

returns:

the dereferenced value or undefined if nonexistent

example:

let value = JsonPointer.get(data, '/legumes/1');
// fragmentId: #/legumes/1

.set(target, pointer, value, force)

Sets the value at the specified pointer on the target. The default behavior is to do nothing if pointer is nonexistent.

arguments:

target : object, required – the target object
pointer : string, required – a JSON pointer in JSON string representation or URI fragment identifier representation
value : any – the value to be set at the specified pointer's path
force : boolean, optional – indicates whether nonexistent paths are created during the call

returns:

The prior value at the pointer's path — therefore, undefined means the pointer's path was nonexistent.

example:

let prior = JsonPointer.set(data, '#/legumes/1/instock', 50);

example force:

let data = {};

JsonPointer.set(data, '#/peter/piper', 'man', true);
JsonPointer.set(data, '#/peter/pan', 'boy', true);
JsonPointer.set(data, '#/peter/pickle', 'dunno', true);

console.log(JSON.stringify(data, null, '  '));

{
  "peter": {
    "piper": "man",
    "pan": "boy",
    "pickle": "dunno"
  }
}

.list(target, fragmentId)

Lists all of the pointers available on the specified target.

See a discussion about cycles in the object graph later in this document if you have interest in how such is dealt with.

arguments:

target : object, required – the target object
fragmentId : boolean, optional – indicates whether fragment identifiers should be listed instead of pointers

returns:

an array of pointer-value pairs

example:

let list = JsonPointer.list(data);

[ ...
  {
    "pointer": "/legumes/2/unit",
    "value": "ea"
  },
  {
    "pointer": "/legumes/2/instock",
    "value": 9340
  },
  {
    "pointer": "/legumes/3/name",
    "value": "plit peas"
  },
  {
    "pointer": "/legumes/3/unit",
    "value": "lbs"
  },
  {
    "pointer": "/legumes/3/instock",
    "value": 8
  }
]

fragmentId example:

let list = JsonPointer.list(data, true);

[ ...
  {
    "fragmentId": "#/legumes/2/unit",
    "value": "ea"
  },
  {
    "fragmentId": "#/legumes/2/instock",
    "value": 9340
  },
  {
    "fragmentId": "#/legumes/3/name",
    "value": "plit peas"
  },
  {
    "fragmentId": "#/legumes/3/unit",
    "value": "lbs"
  },
  {
    "fragmentId": "#/legumes/3/instock",
    "value": 8
  }
]

.flatten(target, fragmentId)

Flattens an object graph (the target) into a single-level object of pointer-value pairs.

arguments:

target : object, required – the target object
fragmentId : boolean, optional – indicates whether fragment identifiers should be listed instead of pointers

returns:

a flattened object of property-value pairs as properties.

example:

let obj = JsonPointer.flatten(data, true);

{ ...
  "#/legumes/1/name": "lima beans",
  "#/legumes/1/unit": "lbs",
  "#/legumes/1/instock": 21,
  "#/legumes/2/name": "black eyed peas",
  "#/legumes/2/unit": "ea",
  "#/legumes/2/instock": 9340,
  "#/legumes/3/name": "plit peas",
  "#/legumes/3/unit": "lbs",
  "#/legumes/3/instock": 8
}

.map(target, fragmentId)

Flattens an object graph (the target) into a Map object.

arguments:

target : object, required – the target object
fragmentId : boolean, optional – indicates whether fragment identifiers should be listed instead of pointers

returns:

a Map object containing key-value pairs where keys are pointers.

example:

let map = JsonPointer.map(data, true);

for (let it of map) {
  console.log(JSON.stringify(it, null, '  '));
}

...
["#/legumes/0/name", "pinto beans"]
["#/legumes/0/unit", "lbs"]
["#/legumes/0/instock", 4 ]
["#/legumes/1/name", "lima beans"]
["#/legumes/1/unit", "lbs"]
["#/legumes/1/instock", 21 ]
["#/legumes/2/name", "black eyed peas"]
["#/legumes/2/unit", "ea"]
["#/legumes/2/instock", 9340 ]
["#/legumes/3/name", "plit peas"]
["#/legumes/3/unit", "lbs"]
["#/legumes/3/instock", 8 ]

.decode(pointer)

Decodes the specified pointer.

arguments:

pointer : string, required – a JSON pointer in JSON string representation or URI fragment identifier representation.

returns:

An array of path segments used as indexers to descend from a root/target object to a referenced value.

example:

let path = JsonPointer.decode('#/legumes/1/instock');

[ "legumes", "1", "instock" ]

decodePointer(pointer)

Decodes the specified pointer.

arguments:

pointer : string, required – a JSON pointer in JSON string representation.

returns:

An array of path segments used as indexers to descend from a root/target object to a referenced value.

example:

let path = decodePointer('/people/wilbur dongleworth/age');

[ "people", "wilbur dongleworth", "age" ]

encodePointer(path)

Encodes the specified path as a JSON pointer in JSON string representation.

arguments:

path : Array, required – an array of path segments

returns:

A JSON pointer in JSON string representation.

example:

let path = encodePointer(['people', 'wilbur dongleworth', 'age']);

"/people/wilbur dongleworth/age"

decodeUriFragmentIdentifier(pointer)

Decodes the specified pointer.

arguments:

pointer : string, required – a JSON pointer in URI fragment identifier representation.

returns:

An array of path segments used as indexers to descend from a root/target object to a referenced value.

example:

let path = decodePointer('#/people/wilbur%20dongleworth/age');

[ "people", "wilbur dongleworth", "age" ]

encodeUriFragmentIdentifier(path)

Encodes the specified path as a JSON pointer in URI fragment identifier representation.

arguments:

path : Array, required - an array of path segments

returns:

A JSON pointer in URI fragment identifier representation.

example:

let path = ptr.encodePointer(['people', 'wilbur dongleworth', 'age']);

"#/people/wilbur%20dongleworth/age"

`JsonPointer` Class

Encapsulates pointer related operations for a specified pointer.

properties:

.path : array – contains the pointer's path segements.
.pointer : string – the pointer's JSON string representation
.uriFragmentIdentifier : string – the pointer's URI fragment identifier representation

methods:

.has(target)

Determins whether the specified target has a value at the pointer's path.

.get(target)

Looks up the specified target's value at the pointer's path if such exists; otherwise undefined.

.set(target, value, force)

Sets the specified target's value at the pointer's path, if such exists.If force is specified (truthy), missing path segments are created and the value is always set at the pointer's path.

arguments:

target : object, required – the target object
value : any – the value to be set at the specified pointer's path
force : boolean, optional – indicates whether nonexistent paths are created during the call

result:

The prior value at the pointer's path — therefore, undefined means the pointer's path was nonexistent.

.concat(target)

Creates new pointer appending target to the current pointer's path

arguments:

target : JsonPointer, array or string, required – the path to be appended to the current path

Performance

This repository has a companion repository that makes some performance comparisons between json-ptr, jsonpointer and json-pointer.

All timings are expressed as nanoseconds:

.flatten(obj)
...
MODULE       | METHOD  | COMPILED | SAMPLES |       AVG | SLOWER
json-pointer | dict    |          | 10      | 464455181 |
json-ptr     | flatten |          | 10      | 770424039 | 65.88%
jsonpointer  | n/a     |          | -       |         - |

.has(obj, pointer)
...
MODULE       | METHOD | COMPILED | SAMPLES | AVG  | SLOWER
json-ptr     | has    | compiled | 1000000 | 822  |
json-ptr     | has    |          | 1000000 | 1747 | 112.53%
json-pointer | has    |          | 1000000 | 2683 | 226.4%
jsonpointer  | n/a    |          | -       | -    |

.has(obj, fragmentId)
...
MODULE       | METHOD | COMPILED | SAMPLES | AVG  | SLOWER
json-ptr     | has    | compiled | 1000000 | 602  |
json-ptr     | has    |          | 1000000 | 1664 | 176.41%
json-pointer | has    |          | 1000000 | 2569 | 326.74%
jsonpointer  | n/a    |          | -       | -    |

.get(obj, pointer)
...
MODULE       | METHOD | COMPILED | SAMPLES | AVG  | SLOWER
json-ptr     | get    | compiled | 1000000 | 590  |
json-ptr     | get    |          | 1000000 | 1676 | 184.07%
jsonpointer  | get    | compiled | 1000000 | 2102 | 256.27%
jsonpointer  | get    |          | 1000000 | 2377 | 302.88%
json-pointer | get    |          | 1000000 | 2585 | 338.14%

.get(obj, fragmentId)
...
MODULE       | METHOD | COMPILED | SAMPLES | AVG  | SLOWER
json-ptr     | get    | compiled | 1000000 | 587  |
json-ptr     | get    |          | 1000000 | 1673 | 185.01%
jsonpointer  | get    | compiled | 1000000 | 2105 | 258.6%
jsonpointer  | get    |          | 1000000 | 2451 | 317.55%
json-pointer | get    |          | 1000000 | 2619 | 346.17%

These results have been elided because there is too much detail in the actual. Your results will vary slightly depending on the resources available where you run it.

It is important to recognize in the performance results that compiled options are faster. As a general rule, you should compile any pointers you'll be using repeatedly.

Consider this example code that queries the flickr API and prints results to the console:

'use strict';

let ptr = require('..'),
  http = require('http'),
  util = require('util');

// A flickr feed, tags surf,pipeline
let feed = 'http://api.flickr.com/services/feeds/photos_public.gne?tags=surf,pipeline&tagmode=all&format=json&jsoncallback=processResponse';

// Compile/prepare the pointers...
let items = ptr.create('#/items');
let author = ptr.create('#/author');
let media = ptr.create('#/media/m');

function processResponse(json) {
  let data = items.get(json);

  if (data && Array.isArray(data)) {
    let images = data.reduce((acc, it) => {
      // Using the prepared pointers to select parts...
      acc.push({
        author: author.get(it),
        media: media.get(it)
      });
      return acc;
    }, []);
    console.log(util.inspect(images, false, 9));
  }
}

http.get(feed, function(res) {
  let data = '';

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

  res.on('end', function() {
    // result is formatted as jsonp... this is for illustration only.
    data = eval(data); // eslint-disable-line no-eval
    processResponse(data);
  });
}).on('error', function(e) {
  console.log('Got error: ' + e.message);
});

[example/real-world.js]

Tests

Tests are written using mocha and expect.js.

npm test

... or ...

mocha

Releases

2019-09-14 — 1.2.0
- Merged new .concat function contributed by @vuwuv, updated dependencies.
2019-03-10 — 1.1.2
- Updated packages to remove critical security concern among dev dependencies'
2016-07-26 — 1.0.1
- Fixed a problem with the Babel configuration
2016-01-12 — 1.0.0
- Rolled major version to 1 to reflect breaking change in .list(obj, fragmentId).
2016-01-02 — 0.3.0
- Retooled for node 4+
- Better compiled pointers
- Unrolled recursive .list function
- Added .map function
- Fully linted
- Lots more tests and examples.
- Documented many previously undocumented features.
2014-10-21 — 0.2.0 Added #list function to enumerate all properties in a graph, producing fragmentId/value pairs.