devalue/src/utils.js

Gets the job done when JSON.stringify can't

import { MAX_ARRAY_INDEX, MAX_ARRAY_LEN } from './constants.js';

const name_chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_$';
const reserved_names =
	/^(?:do|if|in|for|int|let|new|try|var|byte|case|char|else|enum|goto|long|this|void|with|await|break|catch|class|const|final|float|short|super|throw|while|yield|delete|double|export|import|native|return|switch|throws|typeof|boolean|default|extends|finally|package|private|abstract|continue|debugger|function|volatile|interface|protected|transient|implements|instanceof|synchronized)$/;

/** @type {Record<string, string>} */
export const escaped = {
	'<': '\\u003C',
	'\\': '\\\\',
	'\b': '\\b',
	'\f': '\\f',
	'\n': '\\n',
	'\r': '\\r',
	'\t': '\\t',
	'\u2028': '\\u2028',
	'\u2029': '\\u2029'
};

export class DevalueError extends Error {
	/**
	 * @param {string} message
	 * @param {string[]} keys
	 * @param {any} [value] - The value that failed to be serialized
	 * @param {any} [root] - The root value being serialized
	 */
	constructor(message, keys, value, root) {
		super(message);
		this.name = 'DevalueError';
		this.path = keys.join('');
		this.value = value;
		this.root = root;
	}
}

/**
 * Marks a Map key on the path being serialized. The key itself is recorded
 * right after the marker, so nothing is formatted or allocated per entry.
 */
export const MAP_KEY = Symbol();

/**
 * Formats the path recorded on the way to the value being serialized — a
 * property key, an array index, or `MAP_KEY` followed by a Map key — into
 * the segments a `DevalueError` joins. Only runs when an error is raised.
 * @param {any[]} keys
 * @param {(key: any) => string} format_map_key
 * @returns {string[]}
 */
export function format_path(keys, format_map_key) {
	/** @type {string[]} */
	const path = [];

	for (let i = 0; i < keys.length; i += 1) {
		const segment = keys[i];

		if (segment === MAP_KEY) {
			path.push(`.get(${format_map_key(keys[++i])})`);
		} else if (typeof segment === 'number') {
			path.push(`[${segment}]`);
		} else {
			path.push(stringify_key(segment));
		}
	}

	return path;
}

/** @param {any} thing */
export function is_primitive(thing) {
	return thing === null || (typeof thing !== 'object' && typeof thing !== 'function');
}

const object_proto_names = /* @__PURE__ */ Object.getOwnPropertyNames(Object.prototype)
	.sort()
	.join('\0');

/** @param {any} thing */
export function is_plain_object(thing) {
	const proto = Object.getPrototypeOf(thing);

	return (
		proto === Object.prototype ||
		proto === null ||
		Object.getPrototypeOf(proto) === null ||
		Object.getOwnPropertyNames(proto).sort().join('\0') === object_proto_names
	);
}

/** @param {any} thing */
export function get_type(thing) {
	return Object.prototype.toString.call(thing).slice(8, -1);
}

/** @param {any} thing */
export function is_buffer(thing) {
	return typeof Buffer !== 'undefined' && Buffer.isBuffer(thing);
}

/**
 * Emit an array whose storage is not proportional to its declared length.
 * Touching and deleting the largest valid index forces dictionary elements
 * before setting the length; assigning .length on [] can still eagerly allocate.
 * @param {number} length
 */
export function stringify_sparse_array(length) {
	return `(function(a){a[${MAX_ARRAY_INDEX}]=0;delete a[${MAX_ARRAY_INDEX}];a.length=${length};return a}([]))`;
}

/** Returns the compact JavaScript identifier at `index`. @param {number} index */
export function get_name(index) {
	let name = '';

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

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

// characters `stringify_string` always escapes: quote, backslash, `<`, control
// characters and the line/paragraph separators. Surrogates are only escaped
// when unpaired, which `isWellFormed` detects natively, so well-formed pairs
// such as emoji stay on the fast path
const needs_escape = /["<\\\u0000-\u001f\u2028\u2029]/;

// `JSON.stringify` already emits every escape we need except these three,
// which it leaves raw: `<` (so output is safe inside a `<script>` tag) and
// the line/paragraph separators (kept escaped for engines predating ES2019,
// which rejected them in string literals). It also escapes unpaired
// surrogates as `\\udXXX`, so the result survives UTF-8 transport
const json_leaves_raw = /[<\u2028\u2029]/g;

/** @type {Record<string, string>} */
const raw_escapes = { '<': '\\u003C', '\u2028': '\\u2028', '\u2029': '\\u2029' };

/** @param {string} char */
function escape_raw(char) {
	return raw_escapes[char];
}

/** @param {string} str */
export function stringify_string(str) {
	// the common case: nothing to escape, no per-character work
	if (!needs_escape.test(str) && str.isWellFormed()) return `"${str}"`;

	return JSON.stringify(str).replace(json_leaves_raw, escape_raw);
}

// Property names repeat across the values of one call and across calls, so
// their quoted form is cached. Names come from the data being serialized, so
// the cache is bounded in both directions: only short names are kept, and the
// cache is emptied once it holds 1024 of them. Longer names are quoted on
// every visit, like every other string.
const MAX_CACHED_KEY_LENGTH = 64;

/** @type {Map<string, string>} */
const quoted_keys = new Map();

/** @param {string} key */
export function quote_key(key) {
	if (key.length > MAX_CACHED_KEY_LENGTH) return stringify_string(key);

	let quoted = quoted_keys.get(key);

	if (quoted === undefined) {
		if (quoted_keys.size >= 1024) quoted_keys.clear();
		quoted = stringify_string(key);
		quoted_keys.set(key, quoted);
	}

	return quoted;
}

/** @param {Record<string | symbol, any>} object */
export function enumerable_symbols(object) {
	const symbols = Object.getOwnPropertySymbols(object);
	// Own symbols always have a descriptor; the optional chain only satisfies the lib's
	// `PropertyDescriptor | undefined` return type.
	return symbols.length === 0
		? symbols
		: symbols.filter((symbol) => Object.getOwnPropertyDescriptor(object, symbol)?.enumerable);
}

const is_identifier = /^[a-zA-Z_$][a-zA-Z_$0-9]*$/;

/** @param {string} key */
function stringify_key(key) {
	return is_identifier.test(key) ? '.' + key : '[' + JSON.stringify(key) + ']';
}

/** @param {number} n */
export function is_valid_array_index(n) {
	if (!Number.isInteger(n)) return false;
	if (n < 0) return false;
	if (n > MAX_ARRAY_INDEX) return false;
	return true;
}

/** @param {number} n */
export function is_valid_array_len(n) {
	if (!Number.isInteger(n)) return false;
	if (n < 0) return false;
	if (n > MAX_ARRAY_LEN) return false;
	return true;
}

/** @param {string} s */
function is_valid_array_index_string(s) {
	if (s.length === 0) return false;
	if (s.length > 1 && s.charCodeAt(0) === 48) return false; // leading zero
	for (let i = 0; i < s.length; i++) {
		const c = s.charCodeAt(i);
		if (c < 48 || c > 57) return false;
	}
	// by this point we know it's a string of digits, but it has to be within
	// the range of valid array indices
	return is_valid_array_index(+s);
}

/**
 * Returns the length of the leading run of valid array indices in `keys`.
 * @param {readonly string[]} keys
 */
function array_index_cut(keys) {
	for (var i = keys.length - 1; i >= 0; i--) {
		if (is_valid_array_index_string(keys[i])) {
			break;
		}
	}
	return i + 1;
}

/**
 * Finds the populated indices of an array.
 * @param {unknown[]} array
 */
export function valid_array_indices(array) {
	const keys = Object.keys(array);
	keys.length = array_index_cut(keys);
	return keys;
}

/**
 * Given the own enumerable string keys of an array-like value, in property
 * order, returns the leading run of them that are valid array indices.
 *
 * This is the filtering half of the `indicesOf` stringify operation,
 * exposed so that custom operations — which typically already have the keys
 * in hand, e.g. from a foreign runtime — don't have to reimplement it.
 *
 * Does not modify `keys`.
 *
 * @param {readonly string[]} keys
 * @returns {string[]}
 */
export function filter_array_indices(keys) {
	return keys.slice(0, array_index_cut(keys));
}