Convert markdownlint library to an ECMAScript module, replace markdownlint-micromark with micromark, stop publishing (large) markdownlint-browser.js, see https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c for guidance.

lib/cache.mjs

@@ -0,0 +1,62 @@
+// @ts-check
+
+import { getReferenceLinkImageData as helpersGetReferenceLinkImageData } from "../helpers/helpers.cjs";
+import { filterByTypes } from "../helpers/micromark-helpers.cjs";
+
+/** @type {Map<string, object>} */
+const map = new Map();
+let params = undefined;
+
+/**
+ * Initializes (resets) the cache.
+ *
+ * @param {import("./markdownlint.mjs").RuleParams} [p] Rule parameters object.
+ * @returns {void}
+ */
+export function initialize(p) {
+  map.clear();
+  params = p;
+}
+
+/**
+ * Gets a cached object value - computes it and caches it.
+ *
+ * @param {string} name Cache object name.
+ * @param {Function} getValue Getter for object value.
+ * @returns {Object} Object value.
+ */
+function getCached(name, getValue) {
+  if (map.has(name)) {
+    return map.get(name);
+  }
+  const value = getValue();
+  map.set(name, value);
+  return value;
+}
+
+/**
+ * Filters a list of Micromark tokens by type and caches the result.
+ *
+ * @param {import("./markdownlint.mjs").MicromarkTokenType[]} types Types to allow.
+ * @param {boolean} [htmlFlow] Whether to include htmlFlow content.
+ * @returns {import("./markdownlint.mjs").MicromarkToken[]} Filtered tokens.
+ */
+export function filterByTypesCached(types, htmlFlow) {
+  return getCached(
+    // eslint-disable-next-line prefer-rest-params
+    JSON.stringify(arguments),
+    () => filterByTypes(params.parsers.micromark.tokens, types, htmlFlow)
+  );
+}
+
+/**
+ * Gets a reference link and image data object.
+ *
+ * @returns {Object} Reference link and image data object.
+ */
+export function getReferenceLinkImageData() {
+  return getCached(
+    getReferenceLinkImageData.name,
+    () => helpersGetReferenceLinkImageData(params.parsers.micromark.tokens)
+  );
+}