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/md031.mjs

@@ -0,0 +1,62 @@
+// @ts-check
+
+import { addErrorContext, isBlankLine } from "../helpers/helpers.cjs";
+import { getParentOfType } from "../helpers/micromark-helpers.cjs";
+import { filterByTypesCached } from "./cache.mjs";
+
+const codeFencePrefixRe = /^(.*?)[`~]/;
+
+// eslint-disable-next-line jsdoc/valid-types
+/** @typedef {readonly string[]} ReadonlyStringArray */
+
+/**
+ * Adds an error for the top or bottom of a code fence.
+ *
+ * @param {import("./markdownlint.mjs").RuleOnError} onError Error-reporting callback.
+ * @param {ReadonlyStringArray} lines Lines of Markdown content.
+ * @param {number} lineNumber Line number.
+ * @param {boolean} top True iff top fence.
+ * @returns {void}
+ */
+function addError(onError, lines, lineNumber, top) {
+  const line = lines[lineNumber - 1];
+  const [ , prefix ] = line.match(codeFencePrefixRe) || [];
+  const fixInfo = (prefix === undefined) ?
+    undefined :
+    {
+      "lineNumber": lineNumber + (top ? 0 : 1),
+      "insertText": `${prefix.replace(/[^>]/g, " ").trim()}\n`
+    };
+  addErrorContext(
+    onError,
+    lineNumber,
+    line.trim(),
+    undefined,
+    undefined,
+    undefined,
+    fixInfo
+  );
+}
+
+/** @type {import("./markdownlint.mjs").Rule} */
+export default {
+  "names": [ "MD031", "blanks-around-fences" ],
+  "description": "Fenced code blocks should be surrounded by blank lines",
+  "tags": [ "code", "blank_lines" ],
+  "parser": "micromark",
+  "function": function MD031(params, onError) {
+    const listItems = params.config.list_items;
+    const includeListItems = (listItems === undefined) ? true : !!listItems;
+    const { lines } = params;
+    for (const codeBlock of filterByTypesCached([ "codeFenced" ])) {
+      if (includeListItems || !(getParentOfType(codeBlock, [ "listOrdered", "listUnordered" ]))) {
+        if (!isBlankLine(lines[codeBlock.startLine - 2])) {
+          addError(onError, lines, codeBlock.startLine, true);
+        }
+        if (!isBlankLine(lines[codeBlock.endLine]) && !isBlankLine(lines[codeBlock.endLine - 1])) {
+          addError(onError, lines, codeBlock.endLine, false);
+        }
+      }
+    }
+  }
+};