How to limit the rotation of an object in Unity3d?

Question

Unity

There is a 3d object (let's say a cube), using the code:

if (isRotate == true)
        {
            transform.Rotate(Vector3.down * speedRotate * Time.deltaTime);
        }

        if (isRotate == false)
        {
            transform.Rotate(Vector3.up * speedRotate * Time.deltaTime);
        }

How to make a cube rotation limit, searched the entire Internet, nothing helps.

Tried:

if (transform.rotation.y > -90)
            {
                transform.rotation = Quaternion.Euler(0, -90f, 0);
            }

Nothing.

Answer 1

You can try to draw a line and count deviations from it. Another option is to take the standard value and count the deviations and in each frame determine the maximum deviation available (to the edges), but this is too much code for this. The first option is better.