Use a custom promisified setTimeout

src/sharding/Shard.js

@@ -3,7 +3,6 @@ const EventEmitter = require('events');
 const path = require('path');
 const Util = require('../util/Util');
 const { Error } = require('../errors');
-const delayFor = require('util').promisify(setTimeout);
 
 /**
  * A self-contained shard created by the {@link ShardingManager}. Each one has a {@link ChildProcess} that contains
@@ -122,7 +121,7 @@ class Shard extends EventEmitter {
     this.process.removeListener('exit', this._exitListener);
     this.process.kill();
     this._handleExit(false);
-    if (delay > 0) await delayFor(delay);
+    if (delay > 0) await Util.delayFor(delay);
     return this.spawn(waitForReady);
   }
 

src/sharding/ShardingManager.js

@@ -5,7 +5,6 @@ const Shard = require('./Shard');
 const Collection = require('../util/Collection');
 const Util = require('../util/Util');
 const { Error, TypeError, RangeError } = require('../errors');
-const delayFor = require('util').promisify(setTimeout);
 
 /**
  * This is a utility class that makes multi-process sharding of a bot an easy and painless experience.
@@ -132,7 +131,7 @@ class ShardingManager extends EventEmitter {
       const promises = [];
       const shard = this.createShard();
       promises.push(shard.spawn(waitForReady));
-      if (delay > 0 && s !== amount) promises.push(delayFor(delay));
+      if (delay > 0 && s !== amount) promises.push(Util.delayFor(delay));
       await Promise.all(promises); // eslint-disable-line no-await-in-loop
     }
 
@@ -192,7 +191,7 @@ class ShardingManager extends EventEmitter {
     let s = 0;
     for (const shard of this.shards) {
       const promises = [shard.respawn(respawnDelay, waitForReady)];
-      if (++s < this.shards.size && shardDelay > 0) promises.push(delayFor(shardDelay));
+      if (++s < this.shards.size && shardDelay > 0) promises.push(Util.delayFor(shardDelay));
       await Promise.all(promises); // eslint-disable-line no-await-in-loop
     }
     return this.shards;

src/util/Util.js

@@ -366,6 +366,18 @@ class Util {
 
     return dec;
   }
+
+  /**
+   * Creates a Promise that resolves after a specified duration.
+   * @param {number} ms How long to wait before resolving (in milliseconds)
+   * @returns {Promise<void>}
+   * @private
+   */
+  static delayFor(ms) {
+    return new Promise(resolve => {
+      setTimeout(resolve, ms);
+    });
+  }
 }
 
 module.exports = Util;