fix the derp

src/util/Collection.js

@@ -44,6 +44,21 @@ class Collection extends Map {
     return arr[Math.floor(Math.random() * arr.length)];
   }
 
+  /**
+   * If the items in this collection have a delete method (e.g. messages), invoke
+   * the delete method. Returns an array of promises
+   * @return {Array<Promise>}
+   */
+  deleteAll() {
+    const returns = [];
+    for (const item of this.array()) {
+      if (item.delete) {
+        returns.push(item.delete());
+      }
+    }
+    return returns;
+  }
+
   /**
    * The length (size) of this collection.
    * @readonly
@@ -105,6 +120,22 @@ class Collection extends Map {
   _arrayMethod(method, args) {
     return Array.prototype[method].apply(this.array(), args);
   }
+
+  /**
+   * Identical to [Array.filter()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter),
+   * but returns a Collection instead of an Array.
+   * @param {Function} callback the callback used to filter
+   * @param {Object} [thisArg] value to set as this when filtering
+   * @returns {Collection}
+   */
+  filter(...args) {
+    const newArray = this.array().filter(...args);
+    const collection = new Collection();
+    for (const item of newArray) {
+      collection.set(item.id, item);
+    }
+    return collection;
+  }
 }
 
 module.exports = Collection;