class MyFunc {
    _invoke(func_name, a, b) {
        switch (func_name) {
            case 'add':
                return this._add(a, b);
            case 'subtract':
                return this._subtract(a, b);
            default:
                throw new Error(`Invalid func name, ${operation}`);
        }

    }

    _add(a, b) {
        return a + b;
    }

    _subtract(a, b) {
        return a - b;
    }
}

const myFunc = new MyFunc();
console.log(myFunc._invoke("add", 10, 5))