JSFiddle - React, Tailwind, and code Playground

HTML

<p id="B">
 Hello 
</p>

JavaScript

class A {
    constructor(b) {
        this.b = b;
    }
    setTimer(interval) {
        setTimeout(this.b.tick, interval);
    }
}
class B {
    constructor(name){
        this.name = name;
        this.ele = window.document.getElementById('B');
    }
    tick() {
        console.log(this);
        this.ele.innerText += ' ' + this.name;
    }
}

var a = new A(new B("World"));

a.setTimer(1);