Fix the .get() TypeScript return type (#117)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>
sindresorhus · Aug 13, 2020 · 526002e · 526002e
1 parent 1dcfd0d
commit 526002e
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Showing 2 changed files with 12 additions and 7 deletions.
diff --git a/source/index.ts b/source/index.ts
@@ -165,9 +165,12 @@ class Conf<T extends Record<string, any> = Record<string, unknown>> implements I
 	@param key - The key of the item to get.
 	@param defaultValue - The default value if the item does not exist.
 	*/
-	get<Key extends keyof T>(key: Key | string): T[Key] | undefined;
-	get<Key extends keyof T, Default = T[Key]>(key: Key | string, defaultValue: Default): T[Key] | Default;
-	get<Key extends keyof T, Default = T[Key]>(key: Key | string, defaultValue?: Default): Default | undefined {
+	get<Key extends keyof T>(key: Key): T[Key];
+	get<Key extends keyof T>(key: Key, defaultValue: Required<T>[Key]): Required<T>[Key];
+	// This overload is used for dot-notation access.
+	// We exclude `keyof T` as an incorrect type for the default value should not fall through to this overload.
+	get<Key extends string, Value = unknown>(key: Exclude<Key, keyof T>, defaultValue?: Value): Value;
+	get(key: string, defaultValue?: unknown): unknown {
 		if (this.#options.accessPropertiesByDotNotation) {
 			return this._get(key, defaultValue);
 		}

diff --git a/test/index.test-d.ts b/test/index.test-d.ts
@@ -1,5 +1,5 @@
 /* eslint-disable no-new */
-import {expectType, expectAssignable} from 'tsd';
+import {expectType, expectAssignable, expectError} from 'tsd';
 import Conf from '../source';
 
 type UnicornFoo = {
@@ -67,7 +67,7 @@ conf.set({
 	}
 });
 
-expectType<string | undefined>(conf.get('foo'));
+expectType<string>(conf.get('foo'));
 expectType<string>(conf.get('foo', 'bar'));
 conf.delete('foo');
 expectType<boolean>(conf.has('foo'));
@@ -122,11 +122,13 @@ console.log(config.get('unicorn'));
 //=> undefined
 
 // Should be stored type or default
-expectType<boolean | undefined>(config.get('isRainbow'));
+expectType<boolean>(config.get('isRainbow'));
 expectType<boolean>(config.get('isRainbow', false));
 
 expectType<string | undefined>(config.get('unicorn'));
-expectType<string | undefined | number>(config.get('unicorn', 1));
+expectType<string>(config.get('unicorn', 'rainbow'));
+// @ts-expect-error
+expectError<number>(config.get('unicorn', 1));
 
 // --