export default class Mailbox {
  constructor() {
    this.inbox = [];
  }

  enqueue(envelope) {
    this.inbox.push(envelope);
  }

  dequeue() {
    return this.inbox.shift();
  }
}

@@ -78,16 +78,26 @@
 enqueue(
+receiver, 
 envelope
@@ -120,24 +120,36 @@
 ox.push(
+%7B receiver, 
 envelope
 );%0A  %7D%0A%0A
@@ -140,16 +140,18 @@
 envelope
+ %7D
 );%0A  %7D%0A%0A

include receiver to mailbox