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JavaScript

Jeff Lange
Jeff Lange
8,788 Points

Why use elapsedTime, previousTime, and calculations instead of just storing seconds?

The video specifies doing the following:

componentDidMount() {
  this.intervalID = setInterval(() => this.tick(), 100);
}

tick = () => {  
  const now = Date.now();
  this.setState({
    previousTime: now,
    elapsedTime: this.state.elapsedTime + (now - this.state.previousTime)
  })
}

I accomplished the same thing by putting my setInterval function to 1000 (one second), and only specifying the value seconds in my state. So I update going:

componentDidMount() {
  this.intervalID = setInterval(() => this.tick(), 1000);
}

tick = () => {  
  this.setState( prevState => {
    return { seconds: prevState.seconds += 1 }
  });
}

What's the advantage of using previousTime and elapsedTime, plus the calculation? I assume it makes the stopwatch a little more accurate or something.

2 Answers

Steven Parker
Steven Parker
230,230 Points

You're exactly right, calculating the elapsed time gives you an accuracy based on milliseconds.

But in many applications, seconds are perfectly adequate; and as your example shows, simpler to implement.

Jeff Lange
Jeff Lange
8,788 Points

Thanks Steven, I appreciate that