async_hooks: add constructor check to async-hooks

This fixes the async_hooks.AsyncHook constructor such that it throws an
error when provided with falsy values other than undefined.

PR-URL: nodejs#13096
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Andreas Madsen <amwebdk@gmail.com>

lib/async_hooks.js

@@ -77,13 +77,13 @@ function fatalError(e) {
 
 class AsyncHook {
   constructor({ init, before, after, destroy }) {
-    if (init && typeof init !== 'function')
+    if (init !== undefined && typeof init !== 'function')
       throw new TypeError('init must be a function');
-    if (before && typeof before !== 'function')
+    if (before !== undefined && typeof before !== 'function')
       throw new TypeError('before must be a function');
-    if (after && typeof after !== 'function')
+    if (after !== undefined && typeof after !== 'function')
       throw new TypeError('after must be a function');
-    if (destroy && typeof destroy !== 'function')
+    if (destroy !== undefined && typeof destroy !== 'function')
       throw new TypeError('destroy must be a function');
 
     this[init_symbol] = init;

test/parallel/test-async-wrap-constructor.js

@@ -0,0 +1,15 @@
+'use strict';
+require('../common');
+
+// This tests that using falsy values in createHook throws an error.
+
+const assert = require('assert');
+const async_hooks = require('async_hooks');
+
+for (const badArg of [0, 1, false, true, null, 'hello']) {
+  for (const field of ['init', 'before', 'after', 'destroy']) {
+    assert.throws(() => {
+      async_hooks.createHook({ [field]: badArg });
+    }, new RegExp(`^TypeError: ${field} must be a function$`));
+  }
+}