1 files changed, 45 insertions, 0 deletions
diff --git a/devtools/client/debugger/src/utils/async-value.js b/devtools/client/debugger/src/utils/async-value.js
new file mode 100644
index 0000000000..f90b16c5ca
--- /dev/null
+++ b/devtools/client/debugger/src/utils/async-value.js
@@ -0,0 +1,45 @@
+/* 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/>. */
+
+// @flow
+
+export type FulfilledValue<+T> = {|
+  state: "fulfilled",
+  +value: T,
+|};
+export type RejectedValue = {|
+  state: "rejected",
+  value: mixed,
+|};
+export type PendingValue = {|
+  state: "pending",
+|};
+export type SettledValue<+T> = FulfilledValue<T> | RejectedValue;
+export type AsyncValue<+T> = SettledValue<T> | PendingValue;
+
+export function pending(): PendingValue {
+  return { state: "pending" };
+}
+export function fulfilled<+T>(value: T): FulfilledValue<T> {
+  return { state: "fulfilled", value };
+}
+export function rejected(value: mixed): RejectedValue {
+  return { state: "rejected", value };
+}
+
+export function asSettled<T>(
+  value: AsyncValue<T> | null
+): SettledValue<T> | null {
+  return value && value.state !== "pending" ? value : null;
+}
+
+export function isPending(value: AsyncValue<mixed>): boolean %checks {
+  return value.state === "pending";
+}
+export function isFulfilled(value: AsyncValue<mixed>): boolean %checks {
+  return value.state === "fulfilled";
+}
+export function isRejected(value: AsyncValue<mixed>): boolean %checks {
+  return value.state === "rejected";
+}