index.js

'use strict';

const {inspect} = require('util');
const {readFileSync} = require('fs');

const CODE = 'ERR_INVALID_OPT_VALUE_ENCODING';
const ENCODING_ERROR = 'read-json-sync expected the encoding option to be a <string> (defaulting to \'utf8\' if nothing is specified) so as to convert file contents from <Buffer> to <string> before parsing it as JSON';

module.exports = function readJsonSync(...args) {
	const argLen = args.length;

	if (argLen === 2) {
		const options = args[1];
		const isObject = typeof options === 'object';

		if (options === null || (isObject && options.encoding !== undefined && typeof options.encoding !== 'string')) {
			const encoding = options === null ? null : options.encoding;
			const error = new TypeError(`${ENCODING_ERROR}, but a non-string value ${inspect(encoding)} was provided.`);
			error.code = CODE;

			throw error;
		}

		if (options === '' || (isObject && options.encoding === '')) {
			const error = new TypeError(`${ENCODING_ERROR.replace('<', 'non-empty <')}, but '' (empty string) was provided.`);
			error.code = CODE;

			throw error;
		}

		if (isObject || options === undefined) {
			args[1] = {encoding: 'utf8', ...options};
		}
	} else if (argLen === 1) {
		args.push('utf8');
	} else {
		throw new RangeError(`Expected 1 or 2 arguments (path[, options]), but got ${
			argLen === 0 ? 'no' : argLen
		} arguments.`);
	}

	const str = readFileSync(...args);

	return JSON.parse(str.charCodeAt(0) === 65279 /* 0xFEFF */ ? str.slice(1) : str);
};