perf: use extension resolutions only for parent typescript files

Author: pi0

src/jiti.ts

@@ -175,12 +175,17 @@ export default function createJITI(
     for (const ext of _additionalExts) {
       resolved =
         tryResolve(id + ext, options) ||
-        // TODO: Only do this for imports within a typescript parent module
-        tryResolve(id.replace(/\.(c|m)?j(sx?)$/, ".$1t$2"), options) ||
         tryResolve(id + "/index" + ext, options);
       if (resolved) {
         return resolved;
       }
+      // Try resolving .ts files with .js extension
+      if (parentModule?.filename.endsWith(".ts")) {
+        resolved = tryResolve(id.replace(/\.(c|m)?j(sx?)$/, ".$1t$2"), options);
+        if (resolved) {
+          return resolved;
+        }
+      }
     }
     throw err;
   };