From 63961f79dc91d44e937b1d01471e2fa06a5cd6b1 Mon Sep 17 00:00:00 2001
From: Simon Warta <simon@warta.it>
Date: Sun, 9 Oct 2022 18:28:40 +0200
Subject: [PATCH] Add isDefined

---
 CHANGELOG.md                          |  5 +++++
 packages/faucet/src/faucet.ts         |  6 +-----
 packages/utils/src/index.ts           |  2 +-
 packages/utils/src/typechecks.spec.ts | 17 ++++++++++++++++-
 packages/utils/src/typechecks.ts      | 10 ++++++++++
 5 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3a8a755c1e..85e5885bc1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,11 @@ and this project adheres to
 
 ## [Unreleased]
 
+### Added
+
+- @cosmjs/utils: Add `isDefined` which checks for `undefined` in a
+  TypeScript-friendly way.
+
 ## [0.29.1] - 2022-10-09
 
 ### Changed
diff --git a/packages/faucet/src/faucet.ts b/packages/faucet/src/faucet.ts
index bf9bd760c7..b087d38d4f 100644
--- a/packages/faucet/src/faucet.ts
+++ b/packages/faucet/src/faucet.ts
@@ -4,7 +4,7 @@ import {
   SigningStargateClient,
   StargateClient,
 } from "@cosmjs/stargate";
-import { sleep } from "@cosmjs/utils";
+import { isDefined, sleep } from "@cosmjs/utils";
 
 import * as constants from "./constants";
 import { debugAccount, logAccountsState, logSendJob } from "./debugging";
@@ -13,10 +13,6 @@ import { createClients, createWallets } from "./profile";
 import { TokenConfiguration, TokenManager } from "./tokenmanager";
 import { MinimalAccount, SendJob } from "./types";
 
-function isDefined<X>(value: X | undefined): value is X {
-  return value !== undefined;
-}
-
 export class Faucet {
   public static async make(
     apiUrl: string,
diff --git a/packages/utils/src/index.ts b/packages/utils/src/index.ts
index 790c7d277c..624348188b 100644
--- a/packages/utils/src/index.ts
+++ b/packages/utils/src/index.ts
@@ -1,4 +1,4 @@
 export { arrayContentEquals, arrayContentStartsWith } from "./arrays";
 export { assert, assertDefined, assertDefinedAndNotNull } from "./assert";
 export { sleep } from "./sleep";
-export { isNonNullObject, isUint8Array } from "./typechecks";
+export { isDefined, isNonNullObject, isUint8Array } from "./typechecks";
diff --git a/packages/utils/src/typechecks.spec.ts b/packages/utils/src/typechecks.spec.ts
index 5abbac112b..ddbf1209df 100644
--- a/packages/utils/src/typechecks.spec.ts
+++ b/packages/utils/src/typechecks.spec.ts
@@ -1,4 +1,4 @@
-import { isNonNullObject, isUint8Array } from "./typechecks";
+import { isDefined, isNonNullObject, isUint8Array } from "./typechecks";
 
 describe("typechecks", () => {
   describe("isNonNullObject", () => {
@@ -55,4 +55,19 @@ describe("typechecks", () => {
       expect(isUint8Array(new Uint16Array())).toEqual(false);
     });
   });
+
+  describe("isDefined", () => {
+    it("works", () => {
+      expect(isDefined("a")).toEqual(true);
+      expect(isDefined(1234)).toEqual(true);
+      expect(isDefined(null)).toEqual(true);
+      expect(isDefined(undefined)).toEqual(false);
+    });
+
+    it("narrows type of list", () => {
+      const a = ["one", undefined, "two", "three", undefined];
+      const b: string[] = a.filter(isDefined);
+      expect(b).toEqual(["one", "two", "three"]);
+    });
+  });
 });
diff --git a/packages/utils/src/typechecks.ts b/packages/utils/src/typechecks.ts
index c4f56347d2..1d35db5831 100644
--- a/packages/utils/src/typechecks.ts
+++ b/packages/utils/src/typechecks.ts
@@ -30,3 +30,13 @@ export function isUint8Array(data: unknown): data is Uint8Array {
 
   return true;
 }
+
+/**
+ * Checks if input is not undefined in a TypeScript-friendly way.
+ *
+ * This is convenient to use in e.g. `Array.filter` as it will convert
+ * the type of a `Array<Foo | undefined>` to `Array<Foo>`.
+ */
+export function isDefined<X>(value: X | undefined): value is X {
+  return value !== undefined;
+}