75NbF8Ug

1// represent the following API, in other words implement the Events function/class
2
3// scaffold
4class Events {
5  constructor() {
6    this.topicData = {
7    };
8  }
9
10  publish(topic, payload) {
11    if (this.topicData[topic]) {
12      for (let i = 0; i < this.topicData[topic].length; i++)
13        this.topicData[topic][i](payload);
14    }
15  }
16
17  // returns {remove}
18  subscribe(topic, callback) {
19    if (!this.topicData[topic])
20      this.topicData[topic] = [];
21    this.topicData[topic].push(callback);
22    let index = this.topicData[topic].length;
23
24    return {
25      remove: () => {
26        // console.log(index - 1);
27        this.topicData[topic].splice(index - 1, 1);
28      }
29    }
30  }
31
32  publishAll(payload) {
33    for (let key in this.topicData) {
34      this.publish(key, payload);
35    }
36  }
37
38  subscribeOnce(topic, callback) {
39    let topicS = this.subscribe(topic, (payload) => {
40      callback(payload);
41      topicS.remove();
42    });
43
44  }
45
46  // returns a Promise  
47  async subscribeOnceAsync(topic) { }
48}
49
50const events = new Events();
51
52const topicSubscription = events.subscribe('topic', function (payload) { console.log(`this topic has been triggered with ${payload}`) });
53
54events.publish('topic', 'this information');
55// result:
56// this topic has been triggered with this information
57
58const otherTopicSubscription = events.subscribe('topic', function (payload) { console.log(`I have been also summoned with ${payload}`) });
59
60events.publish('topic', 'this information now');
61// result:
62// this topic has been triggered with this information now
63// I have been also summoned with this information now
64
65// topicSubscription.remove();
66
67events.publish('topic', 'another call with this info');
68// result:
69// I have been also summoned with another call with this info
70
71const anotherTopicSubscription = events.subscribe('AnotherTopic', function (payload) { console.log(`new topic, new life with ${payload}`) });
72
73events.publish('AnotherTopic', 'so much to publish!');
74// // result:
75// // new topic, new life with so much to publish!
76
77events.publishAll('every topic deserves to know!');
78
79// // result:
80// // I have been also summoned with every topic deserves to know!
81// // new topic, new life with every topic deserves to know!
82
83events.subscribeOnce('topic', function (payload) { console.log(`this will only execute once with ${payload}`) });
84
85events.publish('topic', 'more stuff!');
86// result:
87// I have been also summoned with more stuff!
88// this will execute only once with more stuff!
89
90
91// events.publish('topic', 'more stuff!');
92// // result:
93// // I have been also summoned with more stuff!
94
95
96// events.subscribeOnceAsync('topic').then(function (payload) { console.log(`this will execute only once with ${payload}`) });
97
98// events.publish('topic', 'more stuff!');
99// // result:
100// // I have been also summoned with more stuff!
101// // this will execute only once with more stuff!
102
103
104// events.publish('topic', 'more stuff again!');
105// // result:
106// // I have been also summoned with more stuff again!