javascript - React 中的倒计时器

Question

我在 JavaScript 中见过很多倒计时器，并希望在 React 中使用一个。

我借用了网上找到的这个函数:

secondsToTime(secs){
    let hours = Math.floor(secs / (60 * 60));

    let divisor_for_minutes = secs % (60 * 60);
    let minutes = Math.floor(divisor_for_minutes / 60);

    let divisor_for_seconds = divisor_for_minutes % 60;
    let seconds = Math.ceil(divisor_for_seconds);

    let obj = {
        "h": hours,
        "m": minutes,
        "s": seconds
    };
    return obj;
  };

然后我自己编写了这段代码

  initiateTimer = () => {
    let timeLeftVar = this.secondsToTime(60);
    this.setState({ timeLeft: timeLeftVar })
  };

  startTimer = () => {
    let interval = setInterval(this.timer, 1000);
    this.setState({ interval: interval });
  };

  timer = () => {
    if (this.state.timeLeft >0){
      this.setState({ timeLeft: this.state.timeLeft -1 });
    }
    else {
      clearInterval(this.state.interval);
      //this.postToSlack();
    }
  };

当前 onclick 会将屏幕上的时间设置为:剩余时间:1 m : 0 s但它不会将其减少到 Time Remaining: 0 m : 59 s 然后 Time Remaining: 0 m : 58 s 等等

我想我需要使用不同的参数再次调用该函数。我该如何去做呢？

编辑:我忘了说，我想要这个功能，以便我可以使用秒到分钟和秒

Answer 1

您必须在剩余的秒数内每秒setState(每次调用间隔时)。这是一个例子:

class Example extends React.Component {
  constructor() {
    super();
    this.state = { time: {}, seconds: 5 };
    this.timer = 0;
    this.startTimer = this.startTimer.bind(this);
    this.countDown = this.countDown.bind(this);
  }

  secondsToTime(secs){
    let hours = Math.floor(secs / (60 * 60));

    let divisor_for_minutes = secs % (60 * 60);
    let minutes = Math.floor(divisor_for_minutes / 60);

    let divisor_for_seconds = divisor_for_minutes % 60;
    let seconds = Math.ceil(divisor_for_seconds);

    let obj = {
      "h": hours,
      "m": minutes,
      "s": seconds
    };
    return obj;
  }

  componentDidMount() {
    let timeLeftVar = this.secondsToTime(this.state.seconds);
    this.setState({ time: timeLeftVar });
  }

  startTimer() {
    if (this.timer == 0 && this.state.seconds > 0) {
      this.timer = setInterval(this.countDown, 1000);
    }
  }

  countDown() {
    // Remove one second, set state so a re-render happens.
    let seconds = this.state.seconds - 1;
    this.setState({
      time: this.secondsToTime(seconds),
      seconds: seconds,
    });
    
    // Check if we're at zero.
    if (seconds == 0) { 
      clearInterval(this.timer);
    }
  }

  render() {
    return(
      <div>
        <button onClick={this.startTimer}>Start</button>
        m: {this.state.time.m} s: {this.state.time.s}
      </div>
    );
  }
}

ReactDOM.render(<Example/>, document.getElementById('View'));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="View"></div>