WIP

More obvious tests

Generic af

Saner tests

WIP

WIP

index.d.ts

@@ -0,0 +1,30 @@
+type Last<T extends readonly unknown[]> = T extends [...any, infer L]
+	? L
+	: never;
+type DropLast<T extends readonly unknown[]> = T extends [...(infer U), any]
+	? U
+	: [];
+
+interface Options {
+	multiArgs: boolean;
+}
+
+type Promisify<TArgs extends readonly unknown[], TOptions extends Options> = (
+	...args: DropLast<TArgs>
+) => Last<TArgs> extends (...args: any) => any
+	? Promise<
+			TOptions extends { multiArgs: false }
+				? Last<Parameters<Last<TArgs>>>
+				: Parameters<Last<TArgs>>
+	  >
+	: never;
+
+declare function pify<
+	TArgs extends readonly unknown[],
+	TOptions extends Options = { multiArgs: false }
+>(
+	input: (...args: TArgs) => any,
+	options?: TOptions
+): Promisify<TArgs, TOptions>;
+
+export = pify;

index.test-d.ts

@@ -0,0 +1,96 @@
+import { expectError, expectType } from "tsd";
+import pify = require(".");
+
+expectError(pify());
+expectError(pify(null));
+expectError(pify(undefined));
+expectError(pify(123));
+expectError(pify("abc"));
+expectError(pify(null, {}));
+expectError(pify(undefined, {}));
+expectError(pify(123, {}));
+expectError(pify("abc", {}));
+
+expectType<never>(pify((v: number) => {})());
+
+// callback with 0 additional params
+declare function fn0(fn: (val: number) => void): void;
+expectType<Promise<number>>(pify(fn0)());
+
+// callback with 1 additional params
+declare function fn1(x: number, fn: (val: number) => void): void;
+expectType<Promise<number>>(pify(fn1)(1));
+
+// callback with 2 additional params
+declare function fn2(x: number, y: number, fn: (val: number) => void): void;
+expectType<Promise<number>>(pify(fn2)(1, 2));
+
+// generics
+
+declare function generic<T>(val: T, fn: (val: T) => void): void;
+declare const genericVal: "hello" | "goodbye";
+expectType<Promise<typeof genericVal>>(pify(generic)(genericVal));
+
+declare function generic10<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(
+	val1: T1,
+	val2: T2,
+	val3: T3,
+	val4: T4,
+	val5: T5,
+	val6: T6,
+	val7: T7,
+	val8: T8,
+	val9: T9,
+	val10: T10,
+	cb: (value: {
+		val1: T1;
+		val2: T2;
+		val3: T3;
+		val4: T4;
+		val5: T5;
+		val6: T6;
+		val7: T7;
+		val8: T8;
+		val9: T9;
+		val10: T10;
+	}) => void
+): void;
+expectType<
+	Promise<{
+		val1: 1;
+		val2: 2;
+		val3: 3;
+		val4: 4;
+		val5: 5;
+		val6: 6;
+		val7: 7;
+		val8: "8";
+		val9: 9;
+		val10: 10;
+	}>
+>(pify(generic10)(1, 2, 3, 4, 5, 6, 7, "8", 9, 10));
+
+// multiArgs
+declare function callback02(cb: (x: number, y: string) => void): void;
+declare function callback12(val: "a", cb: (x: number, y: string) => void): void;
+declare function callback22(
+	val1: "a",
+	val2: "b",
+	cb: (x: number, y: string) => void
+): void;
+
+expectType<Promise<[number, string]>>(pify(callback02, { multiArgs: true })());
+expectType<Promise<[number, string]>>(
+	pify(callback12, { multiArgs: true })("a")
+);
+expectType<Promise<[number, string]>>(
+	pify(callback22, { multiArgs: true })("a", "b")
+);
+
+// overloads
+declare function overloaded(value: number, cb: (value: number) => void): void;
+declare function overloaded(value: string, cb: (value: string) => void): void;
+
+// Chooses last overload
+// See https://github.com/microsoft/TypeScript/issues/32164
+expectType<Promise<string>>(pify(overloaded)(""));

package.json

@@ -16,11 +16,12 @@
 		"node": ">=14.16"
 	},
 	"scripts": {
-		"test": "xo && ava",
+		"test": "xo && ava && tsd",
 		"optimization-test": "node --allow-natives-syntax optimization-test.js"
 	},
 	"files": [
-		"index.js"
+		"index.js",
+		"index.d.ts"
 	],
 	"keywords": [
 		"promisify",
@@ -45,6 +46,8 @@
 	"devDependencies": {
 		"ava": "^4.3.0",
 		"pinkie-promise": "^2.0.1",
+		"tsd": "^0.19.0",
+		"typescript": "^4.5.4",
 		"v8-natives": "^1.2.5",
 		"xo": "^0.49.0"
 	}

tsconfig.json

@@ -0,0 +1,5 @@
+{
+  "compilerOptions": {
+    "strict": true
+  }
+}