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JavaScript

Jeff Lange
Jeff Lange
8,788 Points
Posted by 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
231,141 Points
Steven Parker
Steven Parker
231,141 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
Jeff Lange
Jeff Lange
8,788 Points

Thanks Steven, I appreciate that