51WnsYmX

1// represent the following API, in other words implement the Events function/class
2
3// scaffold
4class Events {
5  constructor() {
6    this.currentTopics = {};
7  }
8  publish(topic, payload) {
9    const toPublish = this.currentTopics[topic];
10    if (toPublish) {
11      debugger;
12      toPublish.forEach(cb => {
13        cb(payload);
14      });
15    }
16  }
17  // returns {remove}
18  subscribe(topic, callback) {
19    if (this.currentTopics[topic]) {
20      this.currentTopics[topic].add(callback);
21    } else {
22      this.currentTopics[topic] = new Set([callback]);
23    }
24    return {
25      remove: () => {
26        console.log("remove");
27        this.currentTopics[topic].delete(callback);
28      }
29    };
30  }
31
32  publishAll(payload) {
33    console.log("publishall");
34    for (let key in this.currentTopics) {
35      const cbSet = this.currentTopics[key];
36      cbSet.forEach(cb => cb(payload));
37    }
38  }
39
40  subscribeOnce(topic, callback) {
41    console.log("subscr once");
42    const newCB = payload => {
43      callback(payload);
44      this.currentTopics[topic].delete(callback);
45    };
46    this.subscribe(topic, newCB);
47  }
48
49  // returns a Promise
50  async subscribeOnceAsync(topic) {
51    console.log("subcribe once async");
52    return new Promise((resolve, reject) => {
53      this.subscribeOnce(topic, resolve);
54    });
55  }
56}
57
58const events = new Events();
59
60const topicSubscription = events.subscribe("topic", function(payload) {
61  console.log(`this topic has been triggered with ${payload}`);
62});
63
64events.publish("topic", "this information");
65// result:
66// this topic has been triggered with this information
67
68const otherTopicSubscription = events.subscribe("topic", function(payload) {
69  console.log(`I have been also summoned with ${payload}`);
70});
71
72events.publish("topic", "this information now");
73// result:
74// this topic has been triggered with this information now
75// I have been also summoned with this information now
76
77topicSubscription.remove();
78
79events.publish("topic", "another call with this info");
80// result:
81// I have been also summoned with another call with this info
82
83const anotherTopicSubscription = events.subscribe("AnotherTopic", function(
84  payload
85) {
86  console.log(`new topic, new life with ${payload}`);
87});
88
89events.publish("AnotherTopic", "so much to publish!");
90// result:
91// new topic, new life with so much to publish!
92
93events.publishAll("every topic deserves to know!");
94
95// result:
96// I have been also summoned with every topic deserves to know!
97// new topic, new life with every topic deserves to know!
98
99events.subscribeOnce("topic", function(payload) {
100  console.log(`this will only execute once with ${payload}`);
101});
102
103events.publish("topic", "more stuff!");
104// result:
105// I have been also summoned with more stuff!
106// this will execute only once with more stuff!
107
108events.publish("topic", "more stuff!");
109// result:
110// I have been also summoned with more stuff!
111
112events.subscribeOnceAsync("topic").then(function(payload) {
113  console.log(`this will execute only once with ${payload}`);
114});
115
116events.publish("topic", "more stuff!");
117// result:
118// I have been also summoned with more stuff!
119// this will execute only once with more stuff!
120
121events.publish("topic", "more stuff again!");
122// result:
123// I have been also summoned with more stuff again!