preact/debug/src/devtools/10/string-table.js

Fast 3kb React-compatible Virtual DOM library.

/**
 * The string table holds a mapping of strings to ids. This saves a lot of space
 * in messaging because we can only need to declare a string once and can later
 * refer to its id. This is especially true for component or element names which
 * expectedoccur multiple times.
 */

/**
 * Convert a string to an id. Works similar to a gzip dictionary.
 * @param {import('./types').StringTable} table
 * @param {string} input
 * @returns {number}
 */
export function getStringId(table, input) {
	if (!table.has(input)) {
		table.set('' + input, table.size + 1);
	}

	return table.get(input);
}

/**
 * Convert string table to something the extension understands
 * @param {import('./types').StringTable} table
 * @returns {number[]}
 */
export function flushTable(table) {
	let ops = [0];

	table.forEach((_, k) => {
		ops[0] += k.length + 1;
		ops.push(k.length, ...encode(k));
	});

	return ops;
}

/**
 * Parse message to strings
 * @param {number[]} data
 */
export function parseTable(data) {
	const len = data[0];
	const strings = [];
	if (len > 0) {
		for (let i = 1; i < len; i++) {
			const strLen = data[i];
			let start = i + 1;
			const end = i + strLen + 1;
			let str = '';
			for (; start < end; start++) {
				str += String.fromCodePoint(data[start]);
			}
			strings.push(str);
			i += strLen;
		}
	}

	return strings;
}

// TODO: Use a proper LRU cache?
/** @type {Map<string, number[]>} */
const encoded = new Map();

/** @type {(s: string) => number} */
const toCodePoint = s => s.codePointAt(0);

/**
 * Convert a string to an array of codepoints
 * @param {string} input
 * @returns {number[]}
 */
export function encode(input) {
	if (!encoded.has(input)) {
		encoded.set(input, input.split('').map(toCodePoint));
	}
	return encoded.get(input);
}