Bug 1873150 - [devtools] Throw in getPreview if evaluated expression has syntax error. r=ochameau,devtools-reviewers.

This will allow us to be notified about expression we shouldn't try to evaluate.

Differential Revision: https://phabricator.services.mozilla.com/D197762

devtools/client/debugger/src/actions/preview.js

@@ -82,9 +82,20 @@ export function getPreview(target, tokenPos, editor) {
       }
     }
 
-    const { result } = await client.evaluate(expression, {
+    const { result, hasException, exception } = await client.evaluate(
-      frameId: selectedFrame.id,
+      expression,
-    });
+      {
+        frameId: selectedFrame.id,
+      }
+    );
+
+    // The evaluation shouldn't return an exception.
+    if (hasException) {
+      const errorClass = exception?.getGrip()?.class || "Error";
+      throw new Error(
+        `Debugger internal exception: Preview for <${expression}> threw a ${errorClass}`
+      );
+    }
 
     const resultGrip = getGrip(result);