7 files changed, 111 insertions, 5 deletions
diff --git a/cli/main.rs b/cli/main.rs
index 3b366306a..da274d8ed 100644
--- a/cli/main.rs
+++ b/cli/main.rs
@@ -46,7 +46,8 @@ use deno_core::error::JsError;
 use deno_core::futures::FutureExt;
 use deno_core::unsync::JoinHandle;
 use deno_npm::resolution::SnapshotFromLockfileError;
-use deno_runtime::fmt_errors::format_js_error;
+use deno_runtime::fmt_errors::format_js_error_with_suggestions;
+use deno_runtime::fmt_errors::FixSuggestion;
 use deno_runtime::tokio_util::create_and_run_current_thread_with_maybe_metrics;
 use deno_terminal::colors;
 use factory::CliFactory;
@@ -336,12 +337,30 @@ fn exit_with_message(message: &str, code: i32) -> ! {
   std::process::exit(code);
 }
 
+fn get_suggestions_for_commonjs_error(e: &JsError) -> Vec<FixSuggestion> {
+  if e.name.as_deref() == Some("ReferenceError") {
+    if let Some(msg) = &e.message {
+      if msg.contains("module is not defined")
+        || msg.contains("exports is not defined")
+      {
+        return vec![
+          FixSuggestion::info("Deno does not support CommonJS modules without `.cjs` extension."),
+          FixSuggestion::hint("Rewrite this module to ESM or change the file extension to `.cjs`."),
+        ];
+      }
+    }
+  }
+
+  vec![]
+}
+
 fn exit_for_error(error: AnyError) -> ! {
   let mut error_string = format!("{error:?}");
   let mut error_code = 1;
 
   if let Some(e) = error.downcast_ref::<JsError>() {
-    error_string = format_js_error(e);
+    let suggestions = get_suggestions_for_commonjs_error(e);
+    error_string = format_js_error_with_suggestions(e, suggestions);
   } else if let Some(SnapshotFromLockfileError::IntegrityCheckFailed(e)) =
     error.downcast_ref::<SnapshotFromLockfileError>()
   {
diff --git a/runtime/fmt_errors.rs b/runtime/fmt_errors.rs
index 4687dbd47..b2cec2a5a 100644
--- a/runtime/fmt_errors.rs
+++ b/runtime/fmt_errors.rs
@@ -20,6 +20,34 @@ struct IndexedErrorReference<'a> {
   index: usize,
 }
 
+#[derive(Debug)]
+enum FixSuggestionKind {
+  Info,
+  Hint,
+}
+
+#[derive(Debug)]
+pub struct FixSuggestion<'a> {
+  kind: FixSuggestionKind,
+  message: &'a str,
+}
+
+impl<'a> FixSuggestion<'a> {
+  pub fn info(message: &'a str) -> Self {
+    Self {
+      kind: FixSuggestionKind::Info,
+      message,
+    }
+  }
+
+  pub fn hint(message: &'a str) -> Self {
+    Self {
+      kind: FixSuggestionKind::Hint,
+      message,
+    }
+  }
+}
+
 struct AnsiColors;
 
 impl deno_core::error::ErrorFormat for AnsiColors {
@@ -129,6 +157,7 @@ fn format_aggregated_error(
         index: nested_circular_reference_index,
       }),
       false,
+      vec![],
     );
 
     for line in error_string.trim_start_matches("Uncaught ").lines() {
@@ -143,6 +172,7 @@ fn format_js_error_inner(
   js_error: &JsError,
   circular: Option<IndexedErrorReference>,
   include_source_code: bool,
+  suggestions: Vec<FixSuggestion>,
 ) -> String {
   let mut s = String::new();
 
@@ -190,7 +220,7 @@ fn format_js_error_inner(
     let error_string = if is_caused_by_circular {
       cyan(format!("[Circular *{}]", circular.unwrap().index)).to_string()
     } else {
-      format_js_error_inner(cause, circular, false)
+      format_js_error_inner(cause, circular, false, vec![])
     };
 
     write!(
@@ -200,6 +230,21 @@ fn format_js_error_inner(
     )
     .unwrap();
   }
+  if !suggestions.is_empty() {
+    write!(s, "\n\n").unwrap();
+    for (index, suggestion) in suggestions.iter().enumerate() {
+      write!(s, "    ").unwrap();
+      match suggestion.kind {
+        FixSuggestionKind::Hint => write!(s, "{} ", cyan("hint:")).unwrap(),
+        FixSuggestionKind::Info => write!(s, "{} ", yellow("info:")).unwrap(),
+      };
+      write!(s, "{}", suggestion.message).unwrap();
+      if index != (suggestions.len() - 1) {
+        writeln!(s).unwrap();
+      }
+    }
+  }
+
   s
 }
 
@@ -211,7 +256,21 @@ pub fn format_js_error(js_error: &JsError) -> String {
       index: 1,
     });
 
-  format_js_error_inner(js_error, circular, true)
+  format_js_error_inner(js_error, circular, true, vec![])
+}
+
+/// Format a [`JsError`] for terminal output, printing additional suggestions.
+pub fn format_js_error_with_suggestions(
+  js_error: &JsError,
+  suggestions: Vec<FixSuggestion>,
+) -> String {
+  let circular =
+    find_recursive_cause(js_error).map(|reference| IndexedErrorReference {
+      reference,
+      index: 1,
+    });
+
+  format_js_error_inner(js_error, circular, true, suggestions)
 }
 
 #[cfg(test)]
diff --git a/tests/specs/run/import_common_js/__test__.jsonc b/tests/specs/run/import_common_js/__test__.jsonc
index a09929cdd..950c7f68c 100644
--- a/tests/specs/run/import_common_js/__test__.jsonc
+++ b/tests/specs/run/import_common_js/__test__.jsonc
@@ -1,6 +1,16 @@
 {
   "steps": [
     { "args": "run -R index.cjs", "output": "index.out" },
-    { "args": "run -R main.ts", "output": "main.out" }
+    { "args": "run -R main.ts", "output": "main.out" },
+    {
+      "args": "run module_error.js",
+      "output": "module_error.out",
+      "exitCode": 1
+    },
+    {
+      "args": "run exports_error.js",
+      "output": "exports_error.out",
+      "exitCode": 1
+    }
   ]
 }
diff --git a/tests/specs/run/import_common_js/exports_error.js b/tests/specs/run/import_common_js/exports_error.js
new file mode 100644
index 000000000..a6a850fe2
--- /dev/null
+++ b/tests/specs/run/import_common_js/exports_error.js
@@ -0,0 +1 @@
+Object.defineProperty(exports, "__esModule", { value: true });
diff --git a/tests/specs/run/import_common_js/exports_error.out b/tests/specs/run/import_common_js/exports_error.out
new file mode 100644
index 000000000..41eda2457
--- /dev/null
+++ b/tests/specs/run/import_common_js/exports_error.out
@@ -0,0 +1,7 @@
+error: Uncaught (in promise) ReferenceError: exports is not defined
+Object.defineProperty(exports, "__esModule", { value: true });
+                      ^
+    at [WILDCARD]exports_error.js:1:23
+
+    info: Deno does not support CommonJS modules without `.cjs` extension.
+    hint: Rewrite this module to ESM or change the file extension to `.cjs`.
diff --git a/tests/specs/run/import_common_js/module_error.js b/tests/specs/run/import_common_js/module_error.js
new file mode 100644
index 000000000..59a3cc0e7
--- /dev/null
+++ b/tests/specs/run/import_common_js/module_error.js
@@ -0,0 +1,3 @@
+module.exports = {
+  foobar: "foobar",
+};
diff --git a/tests/specs/run/import_common_js/module_error.out b/tests/specs/run/import_common_js/module_error.out
new file mode 100644
index 000000000..53a908d29
--- /dev/null
+++ b/tests/specs/run/import_common_js/module_error.out
@@ -0,0 +1,7 @@
+error: Uncaught (in promise) ReferenceError: module is not defined
+module.exports = {
+^
+    at [WILDCARD]module_error.js:1:1
+
+    info: Deno does not support CommonJS modules without `.cjs` extension.
+    hint: Rewrite this module to ESM or change the file extension to `.cjs`.