Bundle Valid ES5 syntax checker in Rollup

rollup.config.js

@@ -1,15 +1,5 @@
-// https://github.com/Turfjs/turf/pull/986
-function typescriptExportsDefault() {
-    return {
-        name: 'typescript-default-export',
-        transformBundle(code) {
-            code = code.trim();
-            const name = code.match(/module.exports = (\w+)/)
-            if (name) code += `\nmodule.exports.default = ${name[1]};\n`;
-            return code;
-        }
-    }
-}
+import typescriptExport from './scripts/rollup-plugin-typescript-export';
+import validES5 from './scripts/rollup-plugin-valid-es5';
 
 export default {
     input: 'index.js',
@@ -18,5 +8,5 @@ export default {
         file: 'main.js',
         format: 'cjs'
     },
-    plugins: [typescriptExportsDefault()]
+    plugins: [typescriptExport(), validES5()]
 };

scripts/rollup-plugin-typescript-export.js

@@ -0,0 +1,12 @@
+// https://github.com/Turfjs/turf/pull/986
+export default function () {
+    return {
+        name: 'typescript-export',
+        transformBundle(code) {
+            code = code.trim();
+            const name = code.match(/module.exports = (\w+)/);
+            if (name) code += `\nmodule.exports.default = ${name[1]};\n`;
+            return code;
+        }
+    };
+}

scripts/rollup-plugin-valid-es5.js

@@ -0,0 +1,24 @@
+export default function () {
+    return {
+        name: 'valid-es5',
+        transformBundle(code) {
+            removeComments(code).match(/[\w\=\>]+/g).forEach(word => {
+                switch (word) {
+                case 'const':
+                case 'let':
+                case '=>':
+                    throw new Error(word + ' is not valid ES5 syntax');
+                }
+            });
+            return code;
+        }
+    };
+}
+
+function removeComments(code) {
+    // Remove comments block comments
+    code = code.replace(/\/\*\*[\w\s*\.@{}|<>,=()[\];\/-]+\*\//g, '');
+    // Remove inline comments
+    code = code.replace(/(\/\/[\s\w()\*\/\\]*)\n/g, '\n');
+    return code;
+}