[Refactor] use async-function for the eval parts

Hopefully fixes #31.

Author: ljharb

getAsyncFunc.d.ts

@@ -1,7 +1,9 @@
+import type { AsyncFunction } from 'async-function';
+
 declare namespace isAsyncFunction {
-    type AsyncFunction = (...args: any[]) => Promise<any>
+    export type { AsyncFunction };
 }
 
-declare function isAsyncFunction(fn: unknown): fn is isAsyncFunction.AsyncFunction;
+declare function isAsyncFunction(fn: unknown): fn is AsyncFunction;
 
 export = isAsyncFunction;

getAsyncFunc.js

@@ -10,10 +10,7 @@ var isFnRegex = safeRegexTest(/^\s*async(?:\s+function(?:\s+|\()|\s*\()/);
 var hasToStringTag = require('has-tostringtag/shams')();
 var getProto = require('get-proto');
 
-var getAsyncFunc = require('./getAsyncFunc');
-
-/** @type {import('.').AsyncFunction | false} */
-var AsyncFunction;
+var getAsyncFunc = require('async-function');
 
 /** @type {import('.')} */
 module.exports = function isAsyncFunction(fn) {
@@ -30,10 +27,6 @@ module.exports = function isAsyncFunction(fn) {
 	if (!getProto) {
 		return false;
 	}
-	if (typeof AsyncFunction === 'undefined') {
-		var asyncFunc = getAsyncFunc();
-		// eslint-disable-next-line no-extra-parens
-		AsyncFunction = asyncFunc ? /** @type {import('.').AsyncFunction} */ (getProto(asyncFunc)) : false;
-	}
-	return AsyncFunction && getProto(fn) === AsyncFunction;
+	var asyncFunc = getAsyncFunc();
+	return asyncFunc && asyncFunc.prototype === getProto(fn);
 };

index.d.ts

@@ -45,6 +45,7 @@
 		"url": "https://github.com/inspect-js/is-async-function/issues"
 	},
 	"dependencies": {
+		"async-function": "^1.0.0",
 		"call-bound": "^1.0.3",
 		"get-proto": "^1.0.1",
 		"has-tostringtag": "^1.0.2",