NumberCounter.js

import React from 'react'

class NumberCounter extends React.Component {

    handle = null
    state = {
        current: 0,
    }
    incrementAmount = 1

    componentDidMount() {
        this.incrementAmount = this.props.target / 60
        this.handleCount()
    }

    componentWillUnmount() {
        this.setState({current: 0})
        clearInterval(this.handle)
    }

    componentWillReceiveProps(nextProps) {
        if(nextProps.target !== this.props.target) {
            this.setState({ current: 0 }, () => {
                this.handleCount()
            })
        }
    }

    handleCount() {
        this.handle = setInterval(() => {
            let current = this.state.current
            const target = this.props.target

            if(current < target) {
                current += this.incrementAmount
                this.setState({ current: Math.floor(current) })
            }
            else {
                this.setState({ current: target })
                clearInterval(this.handle)
            }
        }, 1);
    }

    render() {
        const {
            current,
        } = this.state
        const {
            text,
            target,
        } = this.props

        return (
            <div className="NumberCounter">
                <div className="number">{current}</div>
                <div className="text">{text}</div>
            </div>
        )
    }
}

export default NumberCounter