1 files changed, 83 insertions, 0 deletions
diff --git a/devtools/client/webconsole/test/browser/browser_jsterm_await_helper_dollar_underscore.js b/devtools/client/webconsole/test/browser/browser_jsterm_await_helper_dollar_underscore.js
new file mode 100644
index 0000000000..d947e169d1
--- /dev/null
+++ b/devtools/client/webconsole/test/browser/browser_jsterm_await_helper_dollar_underscore.js
@@ -0,0 +1,83 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Test that $_ works as expected with top-level await expressions.
+
+"use strict";
+requestLongerTimeout(2);
+
+const TEST_URI =
+  "data:text/html;charset=utf-8,<!DOCTYPE html>top-level await + $_";
+
+add_task(async function () {
+  // Enable await mapping.
+  await pushPref("devtools.debugger.features.map-await-expression", true);
+  const hud = await openNewTabAndConsole(TEST_URI);
+
+  info("Evaluate a simple expression to populate $_");
+  await executeAndWaitForResultMessage(hud, `1 + 1`, `2`);
+
+  await executeAndWaitForResultMessage(hud, `$_ + 1`, `3`);
+  ok(true, "$_ works as expected");
+
+  info(
+    "Check that $_ does not get replaced until the top-level await is resolved"
+  );
+  const onAwaitResultMessage = executeAndWaitForResultMessage(
+    hud,
+    `await new Promise(res => setTimeout(() => res([1,2,3, $_]), 1000))`,
+    `Array(4) [ 1, 2, 3, 4 ]`
+  );
+
+  await executeAndWaitForResultMessage(hud, `$_ + 1`, `4`);
+  ok(true, "$_ was not impacted by the top-level await input");
+
+  await onAwaitResultMessage;
+  ok(true, "the top-level await result can use $_ in its returned value");
+
+  await executeAndWaitForResultMessage(
+    hud,
+    `await new Promise(res => setTimeout(() => res([...$_, 5]), 1000))`,
+    `Array(5) [ 1, 2, 3, 4, 5 ]`
+  );
+  ok(true, "$_ is assigned with the result of the top-level await");
+
+  info("Check that awaiting for a rejecting promise does not re-assign $_");
+  await executeAndWaitForErrorMessage(
+    hud,
+    `x = await new Promise((resolve,reject) =>
+      setTimeout(() => reject("await-" + "rej"), 500))`,
+    `await-rej`
+  );
+
+  await executeAndWaitForResultMessage(hud, `$_`, `Array(5) [ 1, 2, 3, 4, 5 ]`);
+  ok(true, "$_ wasn't re-assigned");
+
+  info("Check that $_ gets the value of the last resolved await expression");
+  const delays = [2000, 1000, 4000, 3000];
+  const inputs = delays.map(
+    delay => `await new Promise(
+    r => setTimeout(() => r("await-concurrent-" + ${delay}), ${delay}))`
+  );
+
+  // Let's wait for the message that should be displayed last.
+  const onMessage = waitForMessageByType(
+    hud,
+    "await-concurrent-4000",
+    ".result"
+  );
+  for (const input of inputs) {
+    execute(hud, input);
+  }
+  await onMessage;
+
+  await executeAndWaitForResultMessage(
+    hud,
+    `"result: " + $_`,
+    `"result: await-concurrent-4000"`
+  );
+  ok(
+    true,
+    "$_ was replaced with the last resolving top-level await evaluation result"
+  );
+});