how to get chained methods (builder pattern :3 ) in ES6

fun math.js

class math {
    constructor() {
        this.current = 0;
    }

    add(number) {
        this.current += number;
        return this;
    }

    multiply(number) {
        this.current *= 5;
        return this;
    }

    getCurrent() {
        return this.current;
    }
}

let funMath = new math;

console.log(funMath.getCurrent()); //0

funMath
    .add(5)
    .multiply(5);

console.log(funMath.getCurrent()); //25