JSON-ASTy

Lossless JSON-to-AST Parser and AST-to-JSON Generator

About

JSON-ASTy is a JavaScript library providing a lossless JavaScript Object Notation (JSON) to Abstract Syntax Tree (AST) parser and a corresponding AST to JSON generator. It is intended for cases where one has to read JSON into an AST, manipulate the AST and generate JSON from the AST again while fully preserving the formatting of the original JSON. The AST is based on ASTy-ASTq, and hence can powerfully queried with ASTq, and manipulated with ASTy.

Installation

1$ npm install json-asty

Usage

1const JsonAsty = require("json-asty")
2
3/*  the JSON input  */
4let json = `{
5    "foo": {
6        "bar": true,
7        "baz": 42.0,
8        "quux": [ "test1\\"test2", "test3", 7, true ]
9    }
10}`
11console.log(`JSON (old):\n${json}`)
12
13/*  parse JSON into AST  */
14let ast = JsonAsty.parse(json)
15console.log(`AST Dump (all):\n${JsonAsty.dump(ast, { colors: true })}`)
16
17/*  the AST query  */
18let query = `
19    .// member [
20        ..// member [
21            / string [ pos() == 1 && @value == "foo" ]
22        ]
23        &&
24        / string [ pos() == 1 && @value == "baz" ]
25    ]
26        / * [ pos() == 2 ]
27`
28console.log(`AST Query:\n${query}`)
29
30/*  query AST node  */
31let nodes = ast.query(query)
32let node = nodes[0]
33console.log(`AST Dump (sub, old):\n${node.dump()}`)
34
35/*  manipulate AST node  */
36let nodeNew = node.create("string").set({ value: "TEST" })
37node.parent().del(node).add(nodeNew)
38console.log(`AST Dump (sub, new):\n${node.dump()}`)
39
40/*  unparse AST into JSON  */
41let jsonNew = JsonAsty.unparse(ast)
42console.log(`JSON (new):\n${jsonNew}`)

Output:

JSON (old):
{
    "foo": {
        "bar": true,
        "baz": 42.0,
        "quux": [ "test1\"test2", "test3", 7, true ]
    }
}
AST Dump (all):
object (prolog: "{\n    ", epilog: "}") [1,1]
└── member [2,5]
    ├── string (body: "\"foo\"", value: "foo", epilog: ": ") [2,5]
    └── object (prolog: "{\n        ", epilog: "}\n") [2,12]
        ├── member (epilog: ",\n        ") [3,9]
        │   ├── string (body: "\"bar\"", value: "bar", epilog: ": ") [3,9]
        │   └── boolean (body: "true", value: true) [3,16]
        ├── member (epilog: ",\n        ") [4,9]
        │   ├── string (body: "\"baz\"", value: "baz", epilog: ": ") [4,9]
        │   └── number (body: "42.0", value: 42) [4,16]
        └── member [5,9]
            ├── string (body: "\"quux\"", value: "quux", epilog: ": ") [5,9]
            └── array (prolog: "[ ", epilog: " ]\n    ") [5,17]
                ├── string (body: "\"test1\\\"test2\"", value: "test1\"test2", epilog: ", ") [5,19]
                ├── string (body: "\"test3\"", value: "test3", epilog: ", ") [5,35]
                ├── number (body: "7", value: 7, epilog: ", ") [5,44]
                └── boolean (body: "true", value: true) [5,47]

AST Query:

    .// member [
        ..// member [
            / string [ pos() == 1 && @value == "foo" ]
        ]
        &&
        / string [ pos() == 1 && @value == "baz" ]
    ]
        / * [ pos() == 2 ]

AST Dump (sub, old):
number (body: "42.0", value: 42) [4,16]

AST Dump (sub, new):
number (body: "42.0", value: 42) [4,16]

JSON (new):
{
    "foo": {
        "bar": true,
        "baz": "TEST",
        "quux": [ "test1\"test2", "test3", 7, true ]
    }
}

License

Copyright © 2018-2025 Dr. Ralf S. Engelschall (http://engelschall.com/)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.