7 files changed, 42 insertions, 32 deletions
diff --git a/cli/compat/esm_resolver.rs b/cli/compat/esm_resolver.rs
index f069428e5..0709c66a3 100644
--- a/cli/compat/esm_resolver.rs
+++ b/cli/compat/esm_resolver.rs
@@ -926,6 +926,20 @@ struct PackageConfig {
   typ: String,
 }
 
+pub fn check_if_should_use_esm_loader(
+  main_module: &ModuleSpecifier,
+) -> Result<bool, AnyError> {
+  let s = main_module.as_str();
+  if s.ends_with(".mjs") {
+    return Ok(true);
+  }
+  if s.ends_with(".cjs") {
+    return Ok(false);
+  }
+  let package_config = get_package_scope_config(main_module)?;
+  Ok(package_config.typ == "module")
+}
+
 fn get_package_config(
   path: PathBuf,
   specifier: &str,
@@ -1219,4 +1233,18 @@ mod tests {
     assert!(is_relative_specifier("./foo.js"));
     assert!(!is_relative_specifier("https://deno.land/std/node/http.ts"));
   }
+
+  #[test]
+  fn test_check_if_should_use_esm_loader() {
+    let basic = testdir("basic");
+    let main = Url::from_file_path(basic.join("main.js")).unwrap();
+    assert!(check_if_should_use_esm_loader(&main).unwrap());
+
+    let cjs = Url::from_file_path(basic.join("main.cjs")).unwrap();
+    assert!(!check_if_should_use_esm_loader(&cjs).unwrap());
+
+    let not_esm = testdir("not_esm");
+    let main = Url::from_file_path(not_esm.join("main.js")).unwrap();
+    assert!(!check_if_should_use_esm_loader(&main).unwrap());
+  }
 }
diff --git a/cli/compat/mod.rs b/cli/compat/mod.rs
index 997265f96..3797d7cb4 100644
--- a/cli/compat/mod.rs
+++ b/cli/compat/mod.rs
@@ -8,6 +8,7 @@ use deno_core::located_script_name;
 use deno_core::url::Url;
 use deno_core::JsRuntime;
 
+pub use esm_resolver::check_if_should_use_esm_loader;
 pub(crate) use esm_resolver::NodeEsmResolver;
 
 // TODO(bartlomieju): this needs to be bumped manually for
@@ -86,33 +87,6 @@ fn try_resolve_builtin_module(specifier: &str) -> Option<Url> {
   }
 }
 
-pub(crate) async fn check_if_should_use_esm_loader(
-  js_runtime: &mut JsRuntime,
-  main_module: &str,
-) -> Result<bool, AnyError> {
-  // Decide if we're running with Node ESM loader or CJS loader.
-  let source_code = &format!(
-    r#"(async function checkIfEsm(main) {{
-      const {{ resolveMainPath, shouldUseESMLoader }} = await import("{}");
-      const resolvedMain = resolveMainPath(main);
-      const useESMLoader = shouldUseESMLoader(resolvedMain);
-      return useESMLoader;
-    }})('{}');"#,
-    MODULE_URL_STR.as_str(),
-    escape_for_single_quote_string(main_module),
-  );
-  let result =
-    js_runtime.execute_script(&located_script_name!(), source_code)?;
-  let use_esm_loader_global = js_runtime.resolve_value(result).await?;
-  let use_esm_loader = {
-    let scope = &mut js_runtime.handle_scope();
-    let use_esm_loader_local = use_esm_loader_global.open(scope);
-    use_esm_loader_local.boolean_value(scope)
-  };
-
-  Ok(use_esm_loader)
-}
-
 pub(crate) fn load_cjs_module(
   js_runtime: &mut JsRuntime,
   main_module: &str,
diff --git a/cli/compat/testdata/not_esm/main.js b/cli/compat/testdata/not_esm/main.js
new file mode 100644
index 000000000..347e20832
--- /dev/null
+++ b/cli/compat/testdata/not_esm/main.js
@@ -0,0 +1 @@
+require("foo");
diff --git a/cli/compat/testdata/not_esm/node_modules/foo/index.js b/cli/compat/testdata/not_esm/node_modules/foo/index.js
new file mode 100644
index 000000000..e69de29bb
--- /dev/null
+++ b/cli/compat/testdata/not_esm/node_modules/foo/index.js
diff --git a/cli/compat/testdata/not_esm/node_modules/foo/package.json b/cli/compat/testdata/not_esm/node_modules/foo/package.json
new file mode 100644
index 000000000..a74d52fd3
--- /dev/null
+++ b/cli/compat/testdata/not_esm/node_modules/foo/package.json
@@ -0,0 +1,5 @@
+{
+    "name": "foo",
+    "type": "module",
+    "exports": "./index.js"
+}
diff --git a/cli/compat/testdata/not_esm/package.json b/cli/compat/testdata/not_esm/package.json
new file mode 100644
index 000000000..4b03fc938
--- /dev/null
+++ b/cli/compat/testdata/not_esm/package.json
@@ -0,0 +1,6 @@
+{
+  "name": "bar",
+  "dependencies": {
+    "foo": "1.0.0"
+  }
+}
diff --git a/cli/main.rs b/cli/main.rs
index 67b59a443..d1ee4a012 100644
--- a/cli/main.rs
+++ b/cli/main.rs
@@ -1153,11 +1153,7 @@ async fn run_command(
     // this file.
     worker.execute_side_module(&compat::MODULE_URL).await?;
 
-    let use_esm_loader = compat::check_if_should_use_esm_loader(
-      &mut worker.js_runtime,
-      &main_module.to_file_path().unwrap().display().to_string(),
-    )
-    .await?;
+    let use_esm_loader = compat::check_if_should_use_esm_loader(&main_module)?;
 
     if use_esm_loader {
       // ES module execution in Node compatiblity mode