Fix: MODULE_NOT_FOUND error

Author: mysticatea

lib/foreign-rules/ts.js

@@ -4,7 +4,14 @@
  */
 "use strict"
 
-const rules = require("@typescript-eslint/eslint-plugin").rules
+// This import requires `typescript` package. The MODULE_NOT_FOUND error should
+// be ignored if people want to lint only JS.
+let rules = null
+try {
+    rules = require("@typescript-eslint/eslint-plugin").rules
+} catch (_error) {
+    rules = {}
+}
 
 module.exports = Object.keys(rules).reduce((obj, ruleId) => {
     obj[`ts/${ruleId}`] = rules[ruleId]