Why this clearInterval does not work?

Question

Why does clearInterval not work? When I run it the first time it works, then it outputs "Here", then it creates the second timer that works simultaneously and so on.

     runTimer() {
     let _this = this
     let intervalID
     if (this.state.didTimerRun === false) {
        this.state.didTimerRun = true
        intervalID = setInterval(function() {
            if (_this.state.seconds !== 0) {
                _this.setState({
                    seconds: _this.state.seconds - 1,
                })
            } else if (_this.state.seconds === 0) {
                _this.setState({
                    seconds: 60,
                    workTime: _this.state.workTime - 1
                })
            }
        }, 1000)
    } else {
        console.log('Here')
        clearInterval(intervalID)
        _this.setState({
            workTime: 25,
            seconds: 0,
            didTimerRun: false
        })
    }

}

Answer 1

intervalID is scoped to the runTimer function.

Each time you call runTimer , you use a different runTimer .

You need to declare the variable outside the function if you want it to maintain its values between invocations.