Add Collection.keyArray/firstKey/lastKey/randomKey

src/util/Collection.js

@@ -5,7 +5,7 @@
 class Collection extends Map {
   /**
    * Returns an ordered array of the values of this collection.
-   * @returns {array}
+   * @returns {Array}
    * @example
    * // identical to:
    * Array.from(collection.values());
@@ -14,6 +14,17 @@ class Collection extends Map {
     return Array.from(this.values());
   }
 
+  /**
+   * Returns an ordered array of the keys of this collection.
+   * @returns {Array}
+   * @example
+   * // identical to:
+   * Array.from(collection.keys());
+   */
+  keyArray() {
+    return Array.from(this.keys());
+  }
+
   /**
    * Returns the first item in this collection.
    * @returns {*}
@@ -22,6 +33,14 @@ class Collection extends Map {
     return this.values().next().value;
   }
 
+  /**
+   * Returns the first key in this collection.
+   * @returns {*}
+   */
+  firstKey() {
+    return this.keys().next().value;
+  }
+
   /**
    * Returns the last item in this collection. This is a relatively slow operation,
    * since an array copy of the values must be made to find the last element.
@@ -32,6 +51,16 @@ class Collection extends Map {
     return arr[arr.length - 1];
   }
 
+  /**
+   * Returns the last key in this collection. This is a relatively slow operation,
+   * since an array copy of the keys must be made to find the last element.
+   * @returns {*}
+   */
+  lastKey() {
+    const arr = this.keyArray();
+    return arr[arr.length - 1];
+  }
+
   /**
    * Returns a random item from this collection. This is a relatively slow operation,
    * since an array copy of the values must be made to find a random element.
@@ -42,6 +71,16 @@ class Collection extends Map {
     return arr[Math.floor(Math.random() * arr.length)];
   }
 
+  /**
+   * Returns a random key from this collection. This is a relatively slow operation,
+   * since an array copy of the keys must be made to find a random element.
+   * @returns {*}
+   */
+  randomKey() {
+    const arr = this.keyArray();
+    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