Simple JSON Parser with Loquat https://github.com/susisu/Loquat

json.js

/*
 * Simple JSON Parser
 * http://www.json.org/index.html
 */

var lq = require("loquat");
var util = require("util");

/*
 * Parsers
 */

var json_symbol_colon = lexeme(lq.char(":")).label("colon");
var json_symbol_comma = lexeme(lq.char(",")).label("comma");
var json_symbol_open_brace = lexeme(lq.char("{")).label("open brace");
var json_symbol_close_brace = lexeme(lq.char("}")).label("close brace");
var json_symbol_open_bracket = lexeme(lq.char("[")).label("open bracket");
var json_symbol_close_bracket = lexeme(lq.char("]")).label("close bracket");

var json_value = new lq.LazyParser(function () {
        return lq.choice([
            json_string,
            json_number,
            json_object,
            json_array,
            json_true,
            json_false,
            json_null
        ]);
    })
    .label("value");

var json_string = lexeme(
        lq.manyChar(
            lq.choice([
                lq.noneOf("\"\\\b\f\n\r\t"),
                lq.char("\\").then(
                    lq.fmap(unescapeControlChar)(lq.oneOf("\"\\/bnfrt")),
                    lq.fmap(unescapeUnicodeChar)(
                        lq.char("u").then(lq.fmap(join)(lq.hexDigit.count(4)))
                    )
                )
            ])
        )
        .between(lq.char("\""), lq.char("\""))
    )
    .label("string");

var json_number = lexeme(
        lq.fmap(parseFloat)(
            lq.fmap(join)(
                lq.sequence([
                    lq.option("", lq.char("-")),
                    lq.choice([
                        lq.char("0"),
                        lq.fmap(join)(
                            lq.sequence([
                                lq.oneOf("123456789"),
                                lq.manyChar(lq.digit)
                            ])
                        )
                    ]),
                    lq.option(
                        "",
                        lq.fmap(join)(
                            lq.sequence([
                                lq.char("."),
                                lq.manyChar1(lq.digit)
                            ])
                        )
                    ),
                    lq.option(
                        "",
                        lq.fmap(join)(
                            lq.sequence([
                                lq.oneOf("eE"),
                                lq.option("", lq.oneOf("+-")),
                                lq.manyChar1(lq.digit)
                            ])
                        )
                    )
                ])
            )
        )
    )
    .label("number");

var json_object = lq.sequence([json_string, json_symbol_colon, json_value])
    .sepBy(json_symbol_comma)
    .between(json_symbol_open_brace, json_symbol_close_brace)
    .bind(function (key_values) {
        var obj = {};
        for (var i = 0; i < key_values.length; i ++) {
            obj[key_values[i][0]] = key_values[i][2];
        }
        return lq.pure(obj);
    })
    .label("object");

var json_array = json_value
    .sepBy(json_symbol_comma)
    .between(json_symbol_open_bracket, json_symbol_close_bracket)
    .label("array");

var json_true = lexeme(lq.string("true").try().then(lq.pure(true))).label("true");

var json_false = lexeme(lq.string("false").try().then(lq.pure(false))).label("false");

var json_null = lexeme(lq.string("null").try().then(lq.pure(null))).label("null");

/*
 * Utility Functions
 */

function lexeme (parser) {
    return parser.left(lq.spaces);
}

function join (array) {
    return array.join("");
}

function unescapeControlChar (char) {
    switch (char) {
        case "\"": return "\"";
        case "\\": return "\\";
        case "/" : return "/";
        case "b" : return "\b";
        case "n" : return "\n";
        case "f" : return "\f";
        case "r" : return "\r";
        case "t" : return "\t";
        default  : return char;
    }
}

function unescapeUnicodeChar (codeStr) {
    return String.fromCharCode(parseInt(codeStr, 16));
}

/*
 * Main
 */

var parser = lq.spaces.then(json_value).left(lq.eof);

process.stdin.setEncoding("utf8");
process.stdout.write("> ");
process.stdin.on("readable", function () {
    var chunk = process.stdin.read();
    if (chunk !== null) {
        try {
            console.time("parse");
            var result = lq.parse(parser, "", chunk);
            console.timeEnd("parse");
            if (result.succeeded) {
                process.stdout.write(
                    util.inspect(result.value, { colors: true }) + "\n"
                );
            }
            else {
                process.stdout.write(lq.show(result.error) + "\n");
            }
            process.stdout.write("> ");
        }
        catch (error) {
            console.error(error);
        }
    }
});
process.stdin.on("end", function() {
    process.stdout.write("\nbye\n");
});