index.js

const replaceAll =
  String.prototype.replaceAll ||
  function (searchValue, replaceValue) {
    return this.split(searchValue).join(replaceValue);
  };

const markdownV2EscapeList = [
  "_",
  "*",
  "[",
  "]",
  "(",
  ")",
  "~",
  "`",
  ">",
  "#",
  "+",
  "-",
  "=",
  "|",
  "{",
  "}",
  ".",
  "!",
];

const markdownV1EscapeList = ["_", "*", "`", "["];

const HTMLEscapeMap = {
  "&": "&",
  "<": "&lt;",
  ">": "&gt;",
};

/**
 * @param {String} text
 *
 * @returns {String}
 */
const escapeHTML = (text) =>
  Object.keys(HTMLEscapeMap).reduce(
    (oldText, charToEscape) =>
      replaceAll.call(oldText, charToEscape, HTMLEscapeMap[charToEscape]),
    text
  );

/**
 *
 * @param {String} text
 * @returns {String}
 */
const escapeMarkdown = (text) =>
  markdownV2EscapeList.reduce(
    (oldText, charToEscape) =>
      replaceAll.call(oldText, charToEscape, `\\${charToEscape}`),
    text
  );

/**
 *
 * @param {String} text
 * @returns {String}
 */
const escapeMarkdownV1 = (text) =>
  markdownV1EscapeList.reduce(
    (oldText, charToEscape) =>
      replaceAll.call(oldText, charToEscape, `\\${charToEscape}`),
    text
  );

/**
 * @callback EscapeFunction
 * @param {String} text
 * @returns {String}
 */

/**
 * @callback TagEscapeFunction
 * @param {TemplateStringsArray} template
 * @param {...any} substitutions
 * @returns {String}
 */

/**
 * @private
 * @param {EscapeFunction} escape
 * @returns {TagEscapeFunction}
 */
const escapeTag =
  (escape) =>
  (template, ...substitutions) =>
    String.raw(
      template,
      ...substitutions.map((substitution) =>
        escape(
          String(substitution ?? (substitution === null ? "null" : "undefined"))
        )
      )
    );

/**
 * @type {TagEscapeFunction}
 */
const HTML = escapeTag(escapeHTML);

/**
 * @type {TagEscapeFunction}
 */
const md = escapeTag(escapeMarkdown);

/**
 * @type {TagEscapeFunction}
 */
const mdv1 = escapeTag(escapeMarkdownV1);

module.exports = {
  escapeHTML,
  escapeMarkdown,
  escapeMarkdownV1,
  HTML,
  md,
  mdv1,
};