JSON Query

A small, flexible, and expandable JSON query language.

Try it out on the online playground: https://jsonquerylang.org

• Small: just 4.0 kB when minified and gzipped! The JSON query engine without parse/stringify is only 2.0 kB.
• Feature rich (50+ powerful functions and operators)
• Easy to interoperate with thanks to the intermediate JSON format.
• Expressive
• Expandable

On this page:

• Installation
• Usage
• JavaScript API
• Command line interface (CLI)
• Development
• License

External pages:

• JSON Query Documentation
• JSON Query Function reference
• JSON Query Test Suite

Install the JavaScript library via npm:

npm install @jsonquerylang/jsonquery

A Python implementation can be found here: https://github.com/jsonquerylang/jsonquery-python

import { jsonquery } from '@jsonquerylang/jsonquery'

const data = {
  "friends": [
    { "name": "Chris", "age": 23, "city": "New York" },
    { "name": "Emily", "age": 19, "city": "Atlanta" },
    { "name": "Joe", "age": 32, "city": "New York" },
    { "name": "Kevin", "age": 19, "city": "Atlanta" },
    { "name": "Michelle", "age": 27, "city": "Los Angeles" },
    { "name": "Robert", "age": 45, "city": "Manhattan" },
    { "name": "Sarah", "age": 31, "city": "New York" }
  ]
}

// Get the array containing the friends from the object, filter the friends that live in New York,
// sort them by age, and pick just the name and age out of the objects.
const output = jsonquery(data, `
  .friends 
    | filter(.city == "New York") 
    | sort(.age) 
    | pick(.name, .age)
`)
// output = [
//   { "name": "Chris", "age": 23 },
//   { "name": "Sarah", "age": 31 },
//   { "name": "Joe", "age": 32 }
// ]

// The same query can be written in JSON format instead of the text format.
// Note that the functions `parse` and `stringify` can be used
// to convert from text format to JSON format and vice versa.
jsonquery(data, [
  "pipe",
  ["get", "friends"],
  ["filter", ["eq", ["get", "city"], "New York"]],
  ["sort", ["get", "age"]],
  ["pick", ["get", "name"], ["get", "age"]]
])

The build in functions can be extended with custom functions, like times in the following example:

import { jsonquery } from '@jsonquerylang/jsonquery'

const options = {
  functions: {
    times: (value) => (data) => data.map((item) => item * value)
  }
}

const data = [1, 2, 3]
const result = jsonquery(data, 'times(3)', options)
// [3, 6, 9]

Documentation on the syntax of JSON Query and all supported functions can be found on the website: https://jsonquerylang.org/docs/.

The library exports the following functions:

• jsonquery is the core function of the library, which parses, compiles, and evaluates a query in one go.
• compile to compile and evaluate a query.
• parse to parse a query in text format into JSON.
• stringify to convert a query in JSON into the text format.
• buildFunction a helper function to create a custom function.

The function jsonquery allows to pass data and a query in one go and parse, compile and execute it:

jsonquery(data: JSON, query: string | JSONQuery, options: JSONQueryOptions) : JSON

Here:

• data is the JSON document that will be queried, often an array with objects.
• query is a JSON document containing a JSON query, either the text format or the parsed JSON format.
• options is an optional object that can contain the following properties:

  • functions is an optional map with custom function creators. A function creator has optional arguments as input and must return a function that can be used to process the query data. For example:

    const options = {
      functions: {
        // usage example: 'times(3)'
        times: (value) => (data) => data.map((item) => item * value)
      }
    }

    If the parameters are not a static value but can be a query themselves, the function compile can be used to compile them. For example, the actual implementation of the function filter is the following:

    const options = {
      functions: {
        // usage example: 'filter(.age > 20)'
        filter: (predicate) => {
          const _predicate = compile(predicate)
          return (data) => data.filter(_predicate)
        }
      }
    }

    You can have a look at the source code of the functions in /src/functions.ts for more examples.

  • operators is an optional array definitions for custom operators. Each definition describes the new operator, the name of the function that it maps to, and the desired precedence of the operator: the same, before, or after one of the existing operators (at, before, or after):

    type CustomOperator =
      | { name: string; op: string; at: string; vararg?: boolean, leftAssociative?: boolean }
      | { name: string; op: string; after: string; vararg?: boolean, leftAssociative?: boolean }
      | { name: string; op: string; before: string; vararg?: boolean, leftAssociative?: boolean }

    The defined operators can be used in a text query. Only operators with both a left and right hand side are supported, like a == b. They can only be executed when there is a corresponding function. For example:

    import { buildFunction } from '@jsonquerylang/jsonquery'
    
    const options = {
      // Define a new function "notEqual".
      functions: {
        notEqual: buildFunction((a, b) => a !== b)
      },
    
      // Define a new operator "<>" which maps to the function "notEqual"
      // and has the same precedence as operator "==".
      operators: [
        { name: 'aboutEq', op: '~=', at: '==' }
      ]
    }

    To allow using a chain of multiple operators without parenthesis, like a and b and c, the option leftAssociative can be set true. Without this, an exception will be thrown, which can be solved by using parenthesis like (a and b) and c.

    When the function of the operator supports more than two arguments, like and(a, b, c, ...), the option vararg can be set true. In that case, a chain of operators like a and b and c will be parsed into the JSON Format ["and", a, b, c, ...]. Operators that do not support variable arguments, like 1 + 2 + 3, will be parsed into a nested JSON Format like ["add", ["add", 1, 2], 3].

    All build-in operators and their precedence are listed on the documentation page in the section Operators.

Here an example of using the function jsonquery:

import { jsonquery } from '@jsonquerylang/jsonquery'

const data = [
  { "name": "Chris", "age": 23 },
  { "name": "Emily", "age": 19 },
  { "name": "Joe", "age": 32 }
]

const result = jsonquery(data, ["filter", ["gt", ["get", "age"], 20]])
// result = [
//   { "name": "Chris", "age": 23 },
//   { "name": "Joe", "age": 32 }
// ]

The compile function compiles and executes a query in JSON format. Function parse can be used to parse a text query into JSON before passing it to compile.

compile(query: JSONQuery, options: JSONQueryOptions) => (data: JSON) => JSON

Example:

import { compile } from '@jsonquerylang/jsonquery'

const queryIt = compile(["filter", ["gt", ["get", "age"], 20]])

const data = [
  { "name": "Chris", "age": 23 },
  { "name": "Emily", "age": 19 },
  { "name": "Joe", "age": 32 }
]

const result = queryIt(data)
// result = [
//   { "name": "Chris", "age": 23 },
//   { "name": "Joe", "age": 32 }
// ]

Function parse parses a query in text format into JSON. Function stringify can be used to do the opposite.

parse(query: text, options: JSONQueryParseOptions) : JSONQuery

Example:

import { parse } from '@jsonquerylang/jsonquery'

const text = 'filter(.age > 20)'
const json = parse(text)
// json = ["filter", ["gt", ["get", "age"], 20]]

Function stringify turns a query in JSON format into the equivalent text format. Function parse can be used to parse the text into JSON again.

stringify(query: JSONQuery, options: JSONQueryStringifyOptions) : string

Example:

import { stringify } from '@jsonquerylang/jsonquery'

const json = ["filter", ["gt", ["get", "age"], 20]]
const text = stringify(json)
// text = 'filter(.age > 20)'

The function buildFunction is a helper function to create a custom function. It can only be used for functions (mostly operators), not for methods that need access the previous data as input.

The query engine passes the raw arguments to all functions, and the functions have to compile the arguments themselves when they are dynamic. For example:

const options = {
  functions: {
    notEqual: (a: JSONQuery, b: JSONQuery) => {
      const aCompiled = compile(a)
      const bCompiled = compile(b)

      return (data: unknown) => {
        const aEvaluated = aCompiled(data)
        const bEvaluated = bCompiled(data)

        return aEvaluated !== bEvaluated
      }
    }
  }
}

const data = { x: 2, y: 3}
const result = jsonquery(data, '(.x + .y) <> 6', options) // true

To automatically compile and evaluate the arguments of the function, the helper function buildFunction can be used:

import { jsonquery, buildFunction } from '@jsonquerylang/jsonquery'

const options = {
  functions: {
    notEqual: buildFunction((a: number, b: number) => a !== b)
  }
}

const data = { x: 2, y: 3}
const result = jsonquery(data, '(.x + .y) <> 6', options) // true

When executing a query throws an error, the library attaches a stack to the error message which can give insight in what went wrong. The stack can be found at the property error.jsonquery and has type Array<{ data: unknown, query: JSONQuery }>.

const data = {
  "participants": [
    { "name": "Chris", "age": 23, "scores": [7.2, 5, 8.0] },
    { "name": "Emily", "age": 19 },
    { "name": "Joe", "age": 32, "scores": [6.1, 8.1] }
  ]
}

try {
  jsonquery(data, [
    ["get", "participants"],
    ["map", [["get", "scores"], ["sum"]]]
  ])
} catch (err) {
  console.log(err.jsonquery)
  // error stack:
  // [
  //   {
  //     "data": {
  //       "participants": [
  //         { "name": "Chris", "age": 23, "scores": [7.2, 5, 8.0] },
  //         { "name": "Emily", "age": 19 },
  //         { "name": "Joe", "age": 32, "scores": [6.1, 8.1] }
  //       ]
  //     },
  //     "query": [
  //       ["get", "participants"],
  //       ["map", [["get", "scores"], ["sum"]]]
  //     ]
  //   },
  //   {
  //     "data": [
  //       { "name": "Chris", "age": 23, "scores": [7.2, 5, 8.0] },
  //       { "name": "Emily", "age": 19 },
  //       { "name": "Joe", "age": 32, "scores": [6.1, 8.1] }
  //     ],
  //     "query": ["map", [["get", "scores"], ["sum"]]]
  //   },
  //   {
  //     "data": { "name": "Emily", "age": 19 },
  //     "query": [["get", "scores"], ["sum"]]
  //   },
  //   {
  //     "data" : undefined,
  //     "query": ["sum"]
  //   }
  // ]
}

When jsonquery is installed globally using npm, it can be used on the command line. To install jsonquery globally:

$ npm install -g @jsonquerylang/jsonquery

Usage:

$ jsonquery [query] {OPTIONS}

Options:

--input         Input file name
--query         Query file name
--output        Output file name
--format        Can be "text" (default) or "json"
--indentation   A string containing the desired indentation, 
                like "  " (default) or "    " or "\t". An empty
                string will create output without indentation.
--overwrite     If true, output can overwrite an existing file
--version, -v   Show application version
--help,    -h   Show this message

Example usage:

$ jsonquery --input users.json 'sort(.age)'
$ jsonquery --input users.json 'filter(.city == "Rotterdam") | sort(.age)'
$ jsonquery --input users.json 'sort(.age)' > output.json
$ jsonquery --input users.json 'sort(.age)' --output output.json
$ jsonquery --input users.json --query query.txt
$ jsonquery --input users.json --query query.json --format json
$ cat users.json | jsonquery 'sort(.age)'
$ cat users.json | jsonquery 'sort(.age)' > output.json

To develop, check out the JavaScript repo, install dependencies once, and then use the following scripts:

npm run test
npm run test-ci
npm run lint
npm run format
npm run coverage
npm run build
npm run build-and-test
npm run release-dry-run

Note that a new package is published on npm and GitHub on changes pushed to the main branch. This is done using semantic-release, and we do not use the version number in the package.json file. A changelog can be found by looking at the releases on GitHub.

Released under the ISC license.