From 44c10e7262bd247dfce56590136beebd13ec49c3 Mon Sep 17 00:00:00 2001
From: Alan Choi <alan.choi@sendbird.com>
Date: Thu, 7 Mar 2019 10:13:58 +0900
Subject: [PATCH] keep element type when string literal array passed

When select options is an array of string literal union type, select must return the same type of value.
---
 types/storybook__addon-knobs/index.d.ts                |  1 +
 .../storybook__addon-knobs-tests.tsx                   | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/types/storybook__addon-knobs/index.d.ts b/types/storybook__addon-knobs/index.d.ts
index 3aab101f74..dbfd84a13d 100644
--- a/types/storybook__addon-knobs/index.d.ts
+++ b/types/storybook__addon-knobs/index.d.ts
@@ -52,6 +52,7 @@ export function object<T>(name: string, value: T, groupId?: string): T;
 export function radios<T>(name: string, options: { [s: string]: T }, value?: T, groupId?: string): string;
 
 export function select<T>(name: string, options: { [s: string]: T }, value: T, groupId?: string): T;
+export function select<T extends string>(name: string, options: ReadonlyArray<T>, value: T, groupId?: string): T;
 export function select(name: string, options: ReadonlyArray<string>, value: string, groupId?: string): string;
 
 export function date(name: string, value?: Date, groupId?: string): Date;
diff --git a/types/storybook__addon-knobs/storybook__addon-knobs-tests.tsx b/types/storybook__addon-knobs/storybook__addon-knobs-tests.tsx
index 75ab4c79a9..d09447f75d 100644
--- a/types/storybook__addon-knobs/storybook__addon-knobs-tests.tsx
+++ b/types/storybook__addon-knobs/storybook__addon-knobs-tests.tsx
@@ -94,7 +94,15 @@ stories.add('dynamic knobs', () => {
 });
 
 const readonlyOptionsArray: ReadonlyArray<string> = ['hi'];
-select('With readonly array', readonlyOptionsArray, readonlyOptionsArray[0]);
+select('With readonly string array', readonlyOptionsArray, readonlyOptionsArray[0]);
+
+type StringLiteralType = 'Apple' | 'Banana' | 'Grapes';
+const stringLiteralArray: StringLiteralType[] = ['Apple', 'Banana', 'Grapes'];
+
+let selectedFruit: StringLiteralType;
+
+// type of value returned from `select` must be `StringLiteralType`.
+selectedFruit = select('With string literal array', stringLiteralArray, stringLiteralArray[0]);
 
 const optionsObject = {
   Apple: { taste: 'sweet', color: 'red' },