Add custom rule example to lint JavaScript code blocks using ESLint (fixes #197).

test/lint-javascript.md

@@ -0,0 +1,23 @@
+# Lint JavaScript
+
+<!-- markdownlint-disable MD046 -->
+
+Text
+
+```js
+"use strict";
+
+var x = 0;
+
+console.log(x);
+```
+
+Text
+
+    var y = 0;
+
+Text
+
+Text `undefined` text
+
+Text

test/markdownlint-test.js

@@ -1952,7 +1952,7 @@ module.exports.allBuiltInRulesHaveValidUrl =
 
 module.exports.someCustomRulesHaveValidUrl =
   function someCustomRulesHaveValidUrl(test) {
-    test.expect(6);
+    test.expect(7);
     customRules.all.forEach(function forRule(rule) {
       test.ok(!rule.information ||
         (Object.getPrototypeOf(rule.information) === URL.prototype));
@@ -2886,6 +2886,42 @@ module.exports.customRulesDoc = function customRulesDoc(test) {
   });
 };
 
+module.exports.customRulesLintJavaScript =
+  function customRulesLintJavaScript(test) {
+    test.expect(2);
+    const options = {
+      "customRules": customRules.lintJavaScript,
+      "files": "test/lint-javascript.md"
+    };
+    markdownlint(options, (err, actual) => {
+      test.ifError(err);
+      const expected = {
+        "test/lint-javascript.md": [
+          {
+            "lineNumber": 10,
+            "ruleNames": [ "lint-javascript" ],
+            "ruleDescription": "Rule that lints JavaScript code",
+            "ruleInformation": null,
+            "errorDetail": "Unexpected var, use let or const instead.",
+            "errorContext": "var x = 0;",
+            "errorRange": null
+          },
+          {
+            "lineNumber": 12,
+            "ruleNames": [ "lint-javascript" ],
+            "ruleDescription": "Rule that lints JavaScript code",
+            "ruleInformation": null,
+            "errorDetail": "Unexpected console statement.",
+            "errorContext": "console.log(x);",
+            "errorRange": null
+          }
+        ]
+      };
+      test.deepEqual(actual, expected, "Unexpected issues.");
+      test.done();
+    });
+  };
+
 module.exports.markdownItPluginsSingle =
   function markdownItPluginsSingle(test) {
     test.expect(2);

test/rules/lint-javascript.js

@@ -0,0 +1,34 @@
+// @ts-check
+
+"use strict";
+
+const { filterTokens } = require("markdownlint-rule-helpers");
+const eslint = require("eslint");
+const cliEngine = new eslint.CLIEngine({});
+const linter = new eslint.Linter();
+const languageJavaScript = /js|javascript/i;
+
+module.exports = {
+  "names": [ "lint-javascript" ],
+  "description": "Rule that lints JavaScript code",
+  "tags": [ "test", "lint", "javascript" ],
+  "function": (params, onError) => {
+    filterTokens(params, "fence", (fence) => {
+      if (languageJavaScript.test(fence.info)) {
+        const config = cliEngine.getConfigForFile(params.name);
+        const results = linter.verify(fence.content, config);
+        results.forEach((result) => {
+          const lineNumber = fence.lineNumber + result.line;
+          onError({
+            "lineNumber": lineNumber,
+            "detail": result.message,
+            "context": params.lines[lineNumber - 1]
+          });
+        });
+      }
+    });
+    // Unused:
+    //   filterTokens("code_block"), language unknown
+    //   filterTokens("code_inline"), too brief
+  }
+};

test/rules/rules.js

@@ -14,9 +14,13 @@ module.exports.firstLine = firstLine;
 const lettersEX = require("./letters-E-X");
 module.exports.lettersEX = lettersEX;
 
+const lintJavaScript = require("./lint-javascript");
+module.exports.lintJavaScript = lintJavaScript;
+
 module.exports.all = [
   anyBlockquote,
   everyNLines,
   firstLine,
-  lettersEX
+  lettersEX,
+  lintJavaScript
 ];