webpack/lib/util/parseJson.js

Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
*/

"use strict";

/** @typedef {import("../util/fs").JsonValue} JsonValue */

// Inspired by https://github.com/npm/json-parse-even-better-errors

// Remove byte order marker. This catches EF BB BF (the UTF-8 BOM)
// because the buffer-to-string conversion in `fs.readFileSync()`
// translates it to FEFF, the UTF-16 BOM.
/**
 * @param {string | Buffer} txt text
 * @returns {string} text without BOM
 */
const stripBOM = (txt) => String(txt).replace(/^\uFEFF/, "");

class JSONParseError extends SyntaxError {
	/**
	 * @param {Error} err err
	 * @param {EXPECTED_ANY} raw raw
	 * @param {string} txt text
	 * @param {number=} context context
	 * @param {EXPECTED_FUNCTION=} caller caller
	 */
	constructor(err, raw, txt, context = 20, caller = parseJson) {
		let originalMessage = err.message;
		/** @type {string} */
		let message;
		/** @type {number} */
		let position;

		if (typeof raw !== "string") {
			message = `Cannot parse ${Array.isArray(raw) && raw.length === 0 ? "an empty array" : String(raw)}`;
			position = 0;
		} else if (!txt) {
			message = `${originalMessage} while parsing empty string`;
			position = 0;
		} else {
			// Node 20 puts single quotes around the token and a comma after it
			const UNEXPECTED_TOKEN = /^Unexpected token '?(.)'?(,)? /i;
			const badTokenMatch = originalMessage.match(UNEXPECTED_TOKEN);
			const badIndexMatch = originalMessage.match(/ position\s+(\d+)/i);

			if (badTokenMatch) {
				const h = badTokenMatch[1].charCodeAt(0).toString(16).toUpperCase();
				const hex = `0x${h.length % 2 ? "0" : ""}${h}`;

				originalMessage = originalMessage.replace(
					UNEXPECTED_TOKEN,
					`Unexpected token ${JSON.stringify(badTokenMatch[1])} (${hex})$2 `
				);
			}

			/** @type {number | undefined} */
			let errIdx;

			if (badIndexMatch) {
				errIdx = Number(badIndexMatch[1]);
			} else if (
				// doesn't happen in Node 22+
				/^Unexpected end of JSON.*/i.test(originalMessage)
			) {
				errIdx = txt.length - 1;
			}

			if (errIdx === undefined) {
				message = `${originalMessage} while parsing '${txt.slice(0, context * 2)}'`;
				position = 0;
			} else {
				const start = errIdx <= context ? 0 : errIdx - context;
				const end =
					errIdx + context >= txt.length ? txt.length : errIdx + context;
				const slice = `${start ? "..." : ""}${txt.slice(start, end)}${end === txt.length ? "" : "..."}`;

				message = `${originalMessage} while parsing ${txt === slice ? "" : "near "}${JSON.stringify(slice)}`;
				position = errIdx;
			}
		}

		super(message);

		this.name = "JSONParseError";
		this.systemError = err;
		this.position = position;

		Error.captureStackTrace(this, caller || this.constructor);
	}
}

/**
 * @template [R=JsonValue]
 * @callback ParseJsonFn
 * @param {string} raw text
 * @param {(this: EXPECTED_ANY, key: string, value: EXPECTED_ANY) => EXPECTED_ANY=} reviver reviver
 * @returns {R} parsed JSON
 */

/** @type {ParseJsonFn} */
const parseJson = (raw, reviver) => {
	const txt = stripBOM(raw);

	try {
		return JSON.parse(txt, reviver);
	} catch (err) {
		throw new JSONParseError(/** @type {Error} */ (err), raw, txt);
	}
};

module.exports = parseJson;