Javascript Timer Class

Timer.js

export class Timer {

    constructor() {
        this.offset = 4692;
        this.seconds = 0;
        this.interval = null;
        this.running = false;
        this.history = []
    }

    start() {
        this.history.push({
            action: 'start',
            date: new Date().toISOString()
        });

        this.running = true;
        const startDate = new Date();
        
        this.interval = setInterval( ()=>{
            const currentDate = new Date();
            this.seconds = parseInt((currentDate - startDate) / 1000);
        }, 1000)
    }

    stop() {
        this.history.push({
            action: 'stop',
            date: new Date().toISOString()
        });

        clearInterval(this.interval);
        this.offset = this.offset + this.seconds;
        this.seconds = 0;

        this.running = false;
    }s

    add(seconds) {
        this.history.push({
            action: 'add',
            value: seconds
        });

        this.offset = this.offset + seconds
    }

    elapsed () {
        return this.offset + this.seconds;
    }

    display() {
        var date = new Date(null);
        date.setSeconds( this.elapsed() );

        var result = date.toISOString().substr(11, 8);
        return result
    }
    
    reset() {
        this.history.push({
            action: 'reset',
            date: new Date().toISOString()
        });

        clearInterval(this.interval);
        
        this.offset = 0;
        this.seconds = 0;
        this.running = false;
    }
}