Compile in JS-only mode for files ending in ".js"

packages/ts-plugin/src/index.ts

@@ -160,7 +160,7 @@ const boot: tslib.server.PluginModuleFactory = ({ typescript: ts }) => {
         const { text: expandedText, targetToSourceMap, sourceToTargetMap } = compile({
             source,
             name,
-            typescript: true,
+            typescript: !name.toLowerCase().endsWith('.js'),
             emitError: (message, start, end) => {
                 console.error(`${Syntax.formatPos(start)}-${Syntax.formatPos(end)}: ${message}`);
                 diagnostics.push({ message, start, end });