delay.js

var timeFrame = 500
this.timer = setInterval(() => {
    if (this.state.progress == 1) {
        clearInterval(this.timer);
        setTimeout(() => {
          //When delay is finish do something
        }, timeFrame)
    } else {
        let random = Math.random() * 0.5;
        let progress = this.state.progress + random;
        if (progress > 1) {
            progress = 1;
        }
        this.setState({progress})
    }
}, timeFrame)