🐛 Support async function in isFunction

Author: lambdalisue

is.ts

@@ -278,7 +278,7 @@ function isObjectOfStrict<
  * Return `true` if the type of `x` is `function`.
  */
 export function isFunction(x: unknown): x is (...args: unknown[]) => unknown {
-  return Object.prototype.toString.call(x) === "[object Function]";
+  return x instanceof Function;
 }
 
 /**

is_test.ts

@@ -45,7 +45,7 @@ const examples = {
   boolean: [true, false],
   array: [[], [0, 1, 2], ["a", "b", "c"], [0, "a", true]],
   record: [{}, { a: 0, b: 1, c: 2 }, { a: "a", b: "b", c: "c" }],
-  function: [function a() {}, () => {}],
+  function: [function a() {}, () => {}, async function b() {}, async () => {}],
   null: [null],
   undefined: [undefined],
   symbol: [Symbol("a"), Symbol("b"), Symbol("c")],