@jq-tools/jq

This library intends to implement a fully functional jq interpreter that could be used in the browser or in Node.js.

For more info about the jq language see its official homepage.

Installation

yarn add -E @jq-tools/jq

Usage

Interpreter

From code, you can either use the jq template tag or the evaluate method. It is also possible to use the interpreter from the command line.

Supported features

The interpreter should currently support many of jq's features. However, not everything is supported yet. The following features still lack an implementation:

• Modules
• Most of the formats (except for @base64 and @base64d)
• Most of the built-in filters (to see, which builtins are implemented, please, refer to builtins.spec.ts)
  • Note, however, that at least the following built-in filters are implemented: add/0, all/0, all/1, all/2, any/0, any/1, any/2, del/1, delpaths/1, empty/0, endswith/1 , first/0 , first/1, from_entries/0, group_by/1, has/1, index/1, indices/1, isempty/1, join/1 , keys/0 , last/0, last/1, length/0, limit/2, map/1, match/1, match/2, not/0, nth/1, nth/2 , range/1 , range/2, range/3, rindex/1, round/0, select/1, sort/0, sort_by/1, split/1 , startswith/1, sub/2, sub/3 , test/1, test/2, to_entries/0, tostring/0, type/0, unique/0 , unique_by/1, with_entries/1

jq template tag (jq<In=any, Out=unknown>)

Parses the jq code from the template string and returns a function of shape (input: In[] | IterableIterator<In>) => IterableIterator<Out>. This function can be used to apply the defined jq filter to some input data.

import { jq } from '@jq-tools/jq';

const transform = jq<number, number>`.[] | . * 2`;
Array.from(transform([1, 2, 3]));

Output

[2, 4, 6]

evaluate(ast: ProgAst, input: any[] | IterableIterator<any>): IterableIterator<any>

Evaluates the given jq AST against the provided input.

import { evaluate, parse } from '@jq-tools/jq';

Array.from(evaluate(parse(`.[] | . * 2`), [1, 2, 3]));

Output

[2, 4, 6]

CLI

You can use the jq interpreter from the command line:

echo '5' | yarn jq '.+5' # Outputs: 10

Formatter

format(code: string): string

Formats the provided jq code

import { format } from '@jq-tools/jq';

format(`[.[] | {
"firstName" : .firstName ,
lastName: .surname
}]
`);

Output

[.[] | {
  "firstName": .firstName,
  lastName: .surname,
}]

Code Generator

print(ast: ProgAst): string

Generates code from the provided jq AST.

import { print } from '@jq-tools/jq';

print({
  expr: { expr: { type: 'identity' }, type: 'iterator' },
  type: 'root',
});

Output

.[]

Parser

The parser should be able to handle any jq syntax except for the modules.

For more information about the AST refer to its TypeScript types.

parse(code: string): ProgAst

Parses the provided jq code and returns its AST.

import { parse } from '@jq-tools/jq';

parse('.[].a | {"a": 5 + ., "--\\(. * 2)--": . + 4}');

Output

{
  "expr": {
    "left": {
      "expr": {
        "expr": {
          "type": "identity"
        },
        "type": "iterator"
      },
      "index": "a",
      "type": "index"
    },
    "operator": "|",
    "right": {
      "entries": [
        {
          "key": {
            "interpolated": false,
            "type": "str",
            "value": "a"
          },
          "value": {
            "left": {
              "type": "num",
              "value": 5
            },
            "operator": "+",
            "right": {
              "type": "identity"
            },
            "type": "binary"
          }
        },
        {
          "key": {
            "interpolated": true,
            "parts": [
              "--",
              {
                "left": {
                  "type": "identity"
                },
                "operator": "*",
                "right": {
                  "type": "num",
                  "value": 2
                },
                "type": "binary"
              },
              "--"
            ],
            "type": "str"
          },
          "value": {
            "left": {
              "type": "identity"
            },
            "operator": "+",
            "right": {
              "type": "num",
              "value": 4
            },
            "type": "binary"
          }
        }
      ],
      "type": "object"
    },
    "type": "binary"
  },
  "type": "root"
}

Credits

How to implement a programming language in JavaScript