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JavaScript React Components (2018) Stateful Components and Lifecycle Methods Update the Stopwatch State with componentDidMount()

Ankit Upadhyay
Ankit Upadhyay
556 Points

Update the Stopwatch

Shouldn't the difference of now and this.state.previousTime always becomes zero because as tick() function getting called , we're updating previousTime with now.
So again subtracting , now with this.state.previousTime` shouldn't become zero ?

Here is the code :

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