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/md049-md050.mjs

@@ -0,0 +1,115 @@
+// @ts-check
+
+import { addError } from "../helpers/helpers.cjs";
+import { filterByPredicate, getDescendantsByType } from "../helpers/micromark-helpers.cjs";
+
+const intrawordRe = /^\w$/;
+
+/**
+ * Return the string representation of a emphasis or strong markup character.
+ *
+ * @param {string} markup Emphasis or strong string.
+ * @returns {"asterisk" | "underscore"} String representation.
+ */
+function emphasisOrStrongStyleFor(markup) {
+  switch (markup[0]) {
+    case "*":
+      return "asterisk";
+    default:
+      return "underscore";
+  }
+};
+
+/**
+ * @param {import("./markdownlint.mjs").RuleParams} params Rule parameters.
+ * @param {import("./markdownlint.mjs").RuleOnError} onError Error-reporting callback.
+ * @param {import("micromark-util-types").TokenType} type Token type.
+ * @param {import("micromark-util-types").TokenType} typeSequence Token sequence type.
+ * @param {"*" | "**"} asterisk Asterisk kind.
+ * @param {"_" | "__"} underline Underline kind.
+ * @param {"asterisk" | "consistent" | "underscore"} style Style string.
+ */
+const impl =
+  (params, onError, type, typeSequence, asterisk, underline, style = "consistent") => {
+    const { lines, parsers } = params;
+    const emphasisTokens = filterByPredicate(
+      parsers.micromark.tokens,
+      (token) => token.type === type,
+      (token) => ((token.type === "htmlFlow") ? [] : token.children)
+    );
+    for (const token of emphasisTokens) {
+      const sequences = getDescendantsByType(token, [ typeSequence ]);
+      const startSequence = sequences[0];
+      const endSequence = sequences[sequences.length - 1];
+      if (startSequence && endSequence) {
+        const markupStyle = emphasisOrStrongStyleFor(startSequence.text);
+        if (style === "consistent") {
+          style = markupStyle;
+        }
+        if (style !== markupStyle) {
+          const underscoreIntraword = (style === "underscore") && (
+            intrawordRe.test(
+              lines[startSequence.startLine - 1][startSequence.startColumn - 2]
+            ) ||
+            intrawordRe.test(
+              lines[endSequence.endLine - 1][endSequence.endColumn - 1]
+            )
+          );
+          if (!underscoreIntraword) {
+            for (const sequence of [ startSequence, endSequence ]) {
+              addError(
+                onError,
+                sequence.startLine,
+                `Expected: ${style}; Actual: ${markupStyle}`,
+                undefined,
+                [ sequence.startColumn, sequence.text.length ],
+                {
+                  "editColumn": sequence.startColumn,
+                  "deleteCount": sequence.text.length,
+                  "insertText": (style === "asterisk") ? asterisk : underline
+                }
+              );
+            }
+          }
+        }
+      }
+    }
+  };
+
+/** @type {import("./markdownlint.mjs").Rule[]} */
+export default [
+  {
+    "names": [ "MD049", "emphasis-style" ],
+    "description": "Emphasis style",
+    "tags": [ "emphasis" ],
+    "parser": "micromark",
+    "function": function MD049(params, onError) {
+      return impl(
+        params,
+        onError,
+        "emphasis",
+        "emphasisSequence",
+        "*",
+        "_",
+        params.config.style || undefined
+      );
+    }
+  },
+  {
+    "names": [ "MD050", "strong-style" ],
+    "description": "Strong style",
+    "tags": [ "emphasis" ],
+    "parser": "micromark",
+    "function": function MD050(params, onError) {
+      return impl(
+        params,
+        onError,
+        "strong",
+        "strongSequence",
+        "**",
+        "__",
+        params.config.style || undefined
+      );
+    }
+  }
+];