SOURCE

class Mymath {
    constructor(options) {
        console.log(options);
        this.num = options;
    }

    add(num) {
        this.num += num;
        return this;
    }

    mul(num) {
        this.num *= num;
        return this;
    }

    sub(num) {
        this.num -= num;
        return this;
    }

    run() {
        return this.num;
    }
}

const result = new Mymath(2).add(5).mul(2).sub(7).run();
console.log(result);