uneval.js

import {
	DevalueError,
	escaped,
	get_type,
	is_plain_object,
	is_primitive,
	stringify_string
} from './utils.js';

const chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_$';
const unsafe_chars = /[<>\b\f\n\r\t\0\u2028\u2029]/g;
const reserved =
	/^(?:do|if|in|for|int|let|new|try|var|byte|case|char|else|enum|goto|long|this|void|with|await|break|catch|class|const|final|float|short|super|throw|while|yield|delete|double|export|import|native|return|switch|throws|typeof|boolean|default|extends|finally|package|private|abstract|continue|debugger|function|volatile|interface|protected|transient|implements|instanceof|synchronized)$/;

/**
 * Turn a value into the JavaScript that creates an equivalent value
 * @param {any} value
 * @param {(value: any) => string | void} [replacer]
 */
export function uneval(value, replacer) {
	const counts = new Map();

	/** @type {string[]} */
	const keys = [];

	const custom = new Map();

	/** @param {any} thing */
	function walk(thing) {
		if (typeof thing === 'function') {
			throw new DevalueError(`Cannot stringify a function`, keys);
		}

		if (!is_primitive(thing)) {
			if (counts.has(thing)) {
				counts.set(thing, counts.get(thing) + 1);
				return;
			}

			counts.set(thing, 1);

			if (replacer) {
				const str = replacer(thing);

				if (typeof str === 'string') {
					custom.set(thing, str);
					return;
				}
			}

			const type = get_type(thing);

			switch (type) {
				case 'Number':
				case 'BigInt':
				case 'String':
				case 'Boolean':
				case 'Date':
				case 'RegExp':
					return;

				case 'Array':
					/** @type {any[]} */ (thing).forEach((value, i) => {
						keys.push(`[${i}]`);
						walk(value);
						keys.pop();
					});
					break;

				case 'Set':
					Array.from(thing).forEach(walk);
					break;

				case 'Map':
					for (const [key, value] of thing) {
						keys.push(
							`.get(${is_primitive(key) ? stringify_primitive(key) : '...'})`
						);
						walk(value);
						keys.pop();
					}
					break;

				default:
					if (!is_plain_object(thing)) {
						throw new DevalueError(
							`Cannot stringify arbitrary non-POJOs`,
							keys
						);
					}

					if (Object.getOwnPropertySymbols(thing).length > 0) {
						throw new DevalueError(
							`Cannot stringify POJOs with symbolic keys`,
							keys
						);
					}

					for (const key in thing) {
						keys.push(`.${key}`);
						walk(thing[key]);
						keys.pop();
					}
			}
		}
	}

	walk(value);

	const names = new Map();

	Array.from(counts)
		.filter((entry) => entry[1] > 1)
		.sort((a, b) => b[1] - a[1])
		.forEach((entry, i) => {
			names.set(entry[0], get_name(i));
		});

	/**
	 * @param {any} thing
	 * @returns {string}
	 */
	function stringify(thing) {
		if (names.has(thing)) {
			return names.get(thing);
		}

		if (is_primitive(thing)) {
			return stringify_primitive(thing);
		}

		if (custom.has(thing)) {
			return custom.get(thing);
		}

		const type = get_type(thing);

		switch (type) {
			case 'Number':
			case 'String':
			case 'Boolean':
				return `Object(${stringify(thing.valueOf())})`;

			case 'RegExp':
				return `new RegExp(${stringify_string(thing.source)}, "${
					thing.flags
				}")`;

			case 'Date':
				return `new Date(${thing.getTime()})`;

			case 'Array':
				const members = /** @type {any[]} */ (thing).map((v, i) =>
					i in thing ? stringify(v) : ''
				);
				const tail = thing.length === 0 || thing.length - 1 in thing ? '' : ',';
				return `[${members.join(',')}${tail}]`;

			case 'Set':
			case 'Map':
				return `new ${type}([${Array.from(thing).map(stringify).join(',')}])`;

			default:
				const obj = `{${Object.keys(thing)
					.map((key) => `${safe_key(key)}:${stringify(thing[key])}`)
					.join(',')}}`;
				const proto = Object.getPrototypeOf(thing);
				if (proto === null) {
					return Object.keys(thing).length > 0
						? `Object.assign(Object.create(null),${obj})`
						: `Object.create(null)`;
				}

				return obj;
		}
	}

	const str = stringify(value);

	if (names.size) {
		/** @type {string[]} */
		const params = [];

		/** @type {string[]} */
		const statements = [];

		/** @type {string[]} */
		const values = [];

		names.forEach((name, thing) => {
			params.push(name);

			if (custom.has(thing)) {
				values.push(/** @type {string} */ (custom.get(thing)));
				return;
			}

			if (is_primitive(thing)) {
				values.push(stringify_primitive(thing));
				return;
			}

			const type = get_type(thing);

			switch (type) {
				case 'Number':
				case 'String':
				case 'Boolean':
					values.push(`Object(${stringify(thing.valueOf())})`);
					break;

				case 'RegExp':
					values.push(thing.toString());
					break;

				case 'Date':
					values.push(`new Date(${thing.getTime()})`);
					break;

				case 'Array':
					values.push(`Array(${thing.length})`);
					/** @type {any[]} */ (thing).forEach((v, i) => {
						statements.push(`${name}[${i}]=${stringify(v)}`);
					});
					break;

				case 'Set':
					values.push(`new Set`);
					statements.push(
						`${name}.${Array.from(thing)
							.map((v) => `add(${stringify(v)})`)
							.join('.')}`
					);
					break;

				case 'Map':
					values.push(`new Map`);
					statements.push(
						`${name}.${Array.from(thing)
							.map(([k, v]) => `set(${stringify(k)}, ${stringify(v)})`)
							.join('.')}`
					);
					break;

				default:
					values.push(
						Object.getPrototypeOf(thing) === null ? 'Object.create(null)' : '{}'
					);
					Object.keys(thing).forEach((key) => {
						statements.push(
							`${name}${safe_prop(key)}=${stringify(thing[key])}`
						);
					});
			}
		});

		statements.push(`return ${str}`);

		return `(function(${params.join(',')}){${statements.join(
			';'
		)}}(${values.join(',')}))`;
	} else {
		return str;
	}
}

/** @param {number} num */
function get_name(num) {
	let name = '';

	do {
		name = chars[num % chars.length] + name;
		num = ~~(num / chars.length) - 1;
	} while (num >= 0);

	return reserved.test(name) ? `${name}0` : name;
}

/** @param {string} c */
function escape_unsafe_char(c) {
	return escaped[c] || c;
}

/** @param {string} str */
function escape_unsafe_chars(str) {
	return str.replace(unsafe_chars, escape_unsafe_char);
}

/** @param {string} key */
function safe_key(key) {
	return /^[_$a-zA-Z][_$a-zA-Z0-9]*$/.test(key)
		? key
		: escape_unsafe_chars(JSON.stringify(key));
}

/** @param {string} key */
function safe_prop(key) {
	return /^[_$a-zA-Z][_$a-zA-Z0-9]*$/.test(key)
		? `.${key}`
		: `[${escape_unsafe_chars(JSON.stringify(key))}]`;
}

/** @param {any} thing */
function stringify_primitive(thing) {
	if (typeof thing === 'string') return stringify_string(thing);
	if (thing === void 0) return 'void 0';
	if (thing === 0 && 1 / thing < 0) return '-0';
	const str = String(thing);
	if (typeof thing === 'number') return str.replace(/^(-)?0\./, '$1.');
	if (typeof thing === 'bigint') return thing + 'n';
	return str;
}