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/md009.mjs

@@ -0,0 +1,92 @@
+// @ts-check
+
+import { addError } from "../helpers/helpers.cjs";
+import { addRangeToSet } from "../helpers/micromark-helpers.cjs";
+import { filterByTypesCached } from "./cache.mjs";
+
+/** @type {import("./markdownlint.mjs").Rule} */
+export default {
+  "names": [ "MD009", "no-trailing-spaces" ],
+  "description": "Trailing spaces",
+  "tags": [ "whitespace" ],
+  "parser": "micromark",
+  "function": function MD009(params, onError) {
+    let brSpaces = params.config.br_spaces;
+    brSpaces = Number((brSpaces === undefined) ? 2 : brSpaces);
+    const listItemEmptyLines = !!params.config.list_item_empty_lines;
+    const strict = !!params.config.strict;
+    const codeBlockLineNumbers = new Set();
+    for (const codeBlock of filterByTypesCached([ "codeFenced" ])) {
+      addRangeToSet(codeBlockLineNumbers, codeBlock.startLine + 1, codeBlock.endLine - 1);
+    }
+    for (const codeBlock of filterByTypesCached([ "codeIndented" ])) {
+      addRangeToSet(codeBlockLineNumbers, codeBlock.startLine, codeBlock.endLine);
+    }
+    const listItemLineNumbers = new Set();
+    if (listItemEmptyLines) {
+      for (const listBlock of filterByTypesCached([ "listOrdered", "listUnordered" ])) {
+        addRangeToSet(listItemLineNumbers, listBlock.startLine, listBlock.endLine);
+        let trailingIndent = true;
+        for (let i = listBlock.children.length - 1; i >= 0; i--) {
+          const child = listBlock.children[i];
+          switch (child.type) {
+            case "content":
+              trailingIndent = false;
+              break;
+            case "listItemIndent":
+              if (trailingIndent) {
+                listItemLineNumbers.delete(child.startLine);
+              }
+              break;
+            case "listItemPrefix":
+              trailingIndent = true;
+              break;
+            default:
+              break;
+          }
+        }
+      }
+    }
+    const paragraphLineNumbers = new Set();
+    const codeInlineLineNumbers = new Set();
+    if (strict) {
+      for (const paragraph of filterByTypesCached([ "paragraph" ])) {
+        addRangeToSet(paragraphLineNumbers, paragraph.startLine, paragraph.endLine - 1);
+      }
+      for (const codeText of filterByTypesCached([ "codeText" ])) {
+        addRangeToSet(codeInlineLineNumbers, codeText.startLine, codeText.endLine - 1);
+      }
+    }
+    const expected = (brSpaces < 2) ? 0 : brSpaces;
+    for (let lineIndex = 0; lineIndex < params.lines.length; lineIndex++) {
+      const line = params.lines[lineIndex];
+      const lineNumber = lineIndex + 1;
+      const trailingSpaces = line.length - line.trimEnd().length;
+      if (
+        trailingSpaces &&
+        !codeBlockLineNumbers.has(lineNumber) &&
+        !listItemLineNumbers.has(lineNumber) &&
+        (
+          (expected !== trailingSpaces) ||
+          (strict &&
+            (!paragraphLineNumbers.has(lineNumber) ||
+             codeInlineLineNumbers.has(lineNumber)))
+        )
+      ) {
+        const column = line.length - trailingSpaces + 1;
+        addError(
+          onError,
+          lineNumber,
+          "Expected: " + (expected === 0 ? "" : "0 or ") +
+            expected + "; Actual: " + trailingSpaces,
+          undefined,
+          [ column, trailingSpaces ],
+          {
+            "editColumn": column,
+            "deleteCount": trailingSpaces
+          }
+        );
+      }
+    }
+  }
+};