<script>

    console.log(op(1, 2, add));//

    console.log(op(1, 2, sub));//-1

    console.log(op(1, 2, mul));//

    console.log(op(1, 2, div));//0.5

    function op(num1, num2, back) {

        return back(num1, num2);

    }

    function add(num1, num2) {

        return num1 + num2;

    }

    function sub(num1, num2) {

        return num1 - num2;

    }

    function mul(num1, num2) {

        return num1 * num2;

    }

    function div(num1, num2) {

        return num1 / num2;

    }

</script>