jsonparser2

⚠️ jsonparser2 is in an early pre-release state. Please don't use it in productive applications! ⚠️

Streaming JSON parser.

Installation

npm install @jfhr/jsonparser2

Works in node.js and in the browser!

Usage

jsonparser2 has a callback-based API. You can find more callbacks below!

import { JsonParser } from 'jsonparser2';
const parser = new JsonParser({
    onobjectstart() {
        console.log("Here we go...");
    },
    onkey(key) {
        console.log("Got a key: " + key);
    },
    onstring(value) {
        console.log("Got a value: " + value);
    },
});
parser.write('{"hel');
parser.write('lo": "world"}');
parser.end();

Output:

Here we go...
Got a key: hello
Got a value: world

Parse node.js http/https responses

import * as https from 'https';
import { JsonParser } from 'jsonparser2';

const parser = new JsonParser({
    // Your callbacks here...
});

await new Promise((resolve, reject) => {
    https.get('https://jfhr.de/jsonparser2/Q2063.json', res => {
        res.setEncoding('utf-8');  // or another encoding
        res.on('error', reject);
        res.on('data', chunk => parser.write(decoder.write(chunk)));
        res.on('close', () => {
            parser.end(decoder.end());
            resolve();
        });
    });
});

Parse fetch responses

import { StringDecoder } from "string_decoder";
import { JsonParser } from 'jsonparser2';

const parser = new JsonParser({
    // Your callbacks here...
});

const response = await fetch('https://jfhr.de/jsonparser2/Q2063.json');
const decoder = new StringDecoder('utf-8');  // or another encoding
for await (const chunk of response) {
    parser.write(decoder.write(chunk));
}
parser.write(decoder.end());
parser.end();

Subclassing

You can create a subclass of JsonParser if you want. In your class constructor, call super() and pass your callbacks as a parameter. Note that you need to use the arrow syntax if you want to access instance variables from your callbacks.

class P1163Parser extends JsonParser {
    private isP1163 = false;
    private isP1163Value = false;
    
    constructor() {
        super({
            onkey: key => {
                if (key === 'P1163') {
                    this.isP1163 = true;
                }
                if (this.isP1163 && key === 'value') {
                    this.isP1163Value = true;
                }
            },
            onstring: value => {
                if (this.isP1163Value) {
                    let result = value;
                    console.log('found:', result);
                }
            }
        });
    }
}

const parser = new P1163Parser();

API Reference

Callbacks

Inside all callbacks you can use this to refer to the parser itself, e.g. call this.end() to finish parsing when you find a specific value.

If you use this.write() inside a callback, make sure you don't cause an infinite loop!

onobjectstart: () => void

Called when the start of an object is encountered.

onobjectend: () => void

Called when the end of an object is encountered.

onarraystart: () => void

Called when the start of an array is encountered.

onarrayend: () => void

Called when the end of an array is encountered.

onkey: (key: string) => void

Called when an object key is encountered. The key is passed as a parameter.

onstring: (value: string) => void

Called when a string value is encountered. The value is passed as a parameter.

onnumber: (value: number) => void

Called when a numeric value is encountered. The value is passed as a parameter.

onboolean: (value: boolean) => void

Called when a boolean value is encountered. The value is passed as a parameter.

onnull: () => void

Called when a null value is encountered.

Methods

new JsonParser(cb)

Creates a new parser with the given callbacks. All callbacks are optional.

JsonParser.write(text)

Write the string text to the parser. text must be part of a valid JSON string, otherwise the behavior is undefined!

JsonParser.end()

Close the parser and stop processing. Subsequent calls to write() and end() will be ignored.