1 files changed, 64 insertions, 0 deletions
diff --git a/devtools/client/debugger/src/utils/expressions.js b/devtools/client/debugger/src/utils/expressions.js
new file mode 100644
index 0000000000..4b791af230
--- /dev/null
+++ b/devtools/client/debugger/src/utils/expressions.js
@@ -0,0 +1,64 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { correctIndentation } from "./indentation";
+import { getGrip } from "./evaluation-result";
+
+const UNAVAILABLE_GRIP = { unavailable: true };
+
+/*
+ * wrap the expression input in a try/catch so that it can be safely
+ * evaluated.
+ *
+ * NOTE: we add line after the expression to protect against comments.
+ */
+export function wrapExpression(input) {
+  return correctIndentation(`
+    try {
+      ${input}
+    } catch (e) {
+      e
+    }
+  `);
+}
+
+function isUnavailable(value) {
+  return (
+    value &&
+    !!value.isError &&
+    (value.class === "ReferenceError" || value.class === "TypeError")
+  );
+}
+
+export function getValue(expression) {
+  const { value, exception, error } = expression;
+
+  if (error) {
+    return error;
+  }
+
+  if (!value) {
+    return UNAVAILABLE_GRIP;
+  }
+
+  if (exception) {
+    if (isUnavailable(exception)) {
+      return UNAVAILABLE_GRIP;
+    }
+    return exception;
+  }
+
+  const valueGrip = getGrip(value.result);
+
+  if (valueGrip && typeof valueGrip === "object" && valueGrip.isError) {
+    if (isUnavailable(valueGrip)) {
+      return UNAVAILABLE_GRIP;
+    }
+
+    const { name, message } = valueGrip.preview;
+    return `${name}: ${message}`;
+  }
+
+  return valueGrip;
+}