jjpet

Matching JSON nodes in javascript.

jjpet is a javascript port of Erlang ejpet.

What for ?

Kind of regular expression applied to JSON documents.

• Find if a JSON document has some structural properties, and possibly extract some information.
• Useful to extract small data pieces from large JSON documents.
• Efficient filtering of JSON nodes in real time.

Quick start

Install (using npm)

$ npm install jjpet

Start nodejs REPL

$ node

Check installation is ok

> var jjpet = require('jjpet');
undefined
> var m = jjpet.compile('[*, "foo", *]');
undefined
> jjpet.run(JSON.parse('["foo"]'), m);
{ status: true, captures: {} }

How ?

Express what you want to match using a simple expression language.

Expression syntax

See ejpet expressions

AST

jjpet module exposes parse(pattern) which returns the AST build from pattern. Use it to transform the AST built from a pattern expression, and then use function generate(ast) to produce the corresponding match function.

Captures

API function jjpet.run returns captures as an object where keys are capture names found in the pattern, and values are arrays of matched JSON subparts.

> var jjpet = require('jjpet');
undefined
> var m = jjpet.compile('[*, (?<c1>42), *, (?<c2>43), *]');
undefined
> jjpet.run(JSON.parse('["un", 42, [], 43, {}]'), m);
{ status: true,
  captures: { c1: [ 42 ], c2: [ 43 ] } }

Injections

It is possible to provide some matching values at match-time, through parameter injection forms like (!<param_name>param_type), where param_type may be number, string, boolean and regex. API function ejpet.run allows for passing parameter values as an array which keys are parameter names, and values are parameter values.

> var jjpet = require('jjpet')
undefined
> m = jjpet.compile('(!<howmuch>number)')
undefined
> jjpet.run(JSON.parse('42'), m, {howmuch: 42})
{ status: true, captures: {} }
> jjpet.run(JSON.parse('43'), m, {howmuch: 42})
{ status: false, captures: {} }
> jjpet.run(JSON.parse('42'), m, {howmuch: 43})
{ status: false, captures: {} }

Captures AND injections

jjpet allows combination of both captures and injections.

> var jjpet = require('jjpet')
undefined
> m = jjpet.compile('[*, (!<howmuch>number), *, (?<struct>{"number":(!<howmuch>number)}), *]')
undefined
> jjpet.run(JSON.parse('[41, 42, 43, {"number": 42}]'), m, {howmuch: 42})
{ status: true,
  captures: { struct : [ { number: 42 } ] } }
> jjpet.run(JSON.parse('[41, 43, {"number": 42}]'), m, {howmuch: 42})
{ status: false, captures: {} }