事件驱动编程入门

1const EventEmitter = require('events');
2
3// Create an instance of EventEmitter
4const myEmitter = new EventEmitter();
5
6// Add an event listener
7myEmitter.on('greet', (name) => {
8    console.log(`Hello, ${name}!`);
9});
10
11// Emit the event
12myEmitter.emit('greet', 'Alice');

Output

1Time remaining: 5 seconds
2Time remaining: 4 seconds
3Time remaining: 3 seconds
4Time remaining: 2 seconds
5Time remaining: 1 second
6Countdown complete!

显示答案

以下是 index.js 的代码：

答案：使用 EventEmitter 构建动态倒计时器

1const EventEmitter = require('events');
2
3// Create an instance of EventEmitter
4const countdown = new EventEmitter();
5
6// Add listeners
7countdown.on('tick', (time) => {
8    console.log(`Time remaining: ${time} seconds`);
9});
10
11countdown.on('end', () => {
12    console.log('Countdown complete!');
13});
14
15// Function to start the countdown
16function startCountdown(seconds) {
17    let remaining = seconds;
18
19    const interval = setInterval(() => {
20        if (remaining > 0) {
21            countdown.emit('tick', remaining);
22            remaining--;
23        } else {
24            clearInterval(interval);
25            countdown.emit('end');
26        }
27    }, 1000);
28}
29
30// Start a 5-second countdown
31startCountdown(5);

• Line 1: The events module is imported.

• Line 4: An EventEmitter instance is created to handle countdown events.

• Lines 7–9: A listener is added for the tick event to log the remaining time.

• Lines 11–13: A listener is added for the end event to log a completion message.

• Line 16–22: The startCountdown function initializes the countdown and uses setInterval to emit the tick event every second.

• Lines 23–26: When the countdown reaches zero, the end event is emitted, and the interval is cleared.

• Line 1: The events module is imported.

• Line 4: An EventEmitter instance is created to handle countdown events.

• Lines 7–9: A listener is added for the tick event to log the remaining time.

• Lines 11–13: A listener is added for the end event to log a completion message.

• Line 16–22: The startCountdown function initializes the countdown and uses setInterval to emit the tick event every second.

• Lines 23–26: When the countdown reaches zero, the end event is emitted, and the interval is cleared.

显示提示

• Use require('events') to include the events module and create an instance of EventEmitter for managing custom events.

• Use .on to define listeners for events like tick (for displaying the remaining time) and end (for signaling the countdown completion).

• Use .emit to trigger the tick event with the remaining time as an argument and the end event when the countdown ends.

• Use setInterval to create a loop that decrements the countdown every second, stopping it with clearInterval when time runs out.