check that options.varName is a valid JS identifier

src/compile.ts

@@ -1,6 +1,6 @@
 import compileToString from './compile-string'
 import { getConfig } from './config'
-import { asyncFunc } from './utils'
+import { asyncFunc, isValidJSIdentifier } from './utils'
 import SqrlErr from './err'
 
 /* TYPES */
@@ -26,6 +26,9 @@ export default function compile (str: string, env?: PartialConfig): TemplateFunc
       throw SqrlErr("This environment doesn't support async/await")
     }
   }
+  if (options.varName && isValidJSIdentifier(options.varName) === false) {
+    throw SqrlErr("options.varName must be a valid JS identifier")
+  }
 
   /* END ASYNC HANDLING */
   try {

src/utils.ts

@@ -113,4 +113,9 @@ function trimWS (
   return str
 }
 
-export { trimWS }
+// credit to pugjs/pug
+function isValidJSIdentifier (str: string) {
+  return /^[a-zA-Z_$][a-zA-Z0-9_$]*$/.test(name);
+}
+
+export { trimWS, isValidJSIdentifier }