My jump code seems to be broken, the character's flags for jumping appear to be working strangely.

 var moveSpeed:float = 1.0;
 var y : float;
 var isJumping:byte = 0;
 var isOnGround:byte = 1;
 var maxHeight:int = 2;
 
 function Update () 
 {//if the player is eligible to jump, pressing W will send them upwards and make them inelegible to jump until they have landed.
     if(isOnGround == 1)
     {
         if(Input.GetButton("forward"))
         {
             rigidbody.AddForce(Vector3.up*50);
             isOnGround = 0;
         }
         
     }
     if(Input.GetButton("forward") == false)
     {
         isJumping = 0; //the player is not jumping if the button is not pressed
     }
     
 
     if(transform.position.y <= 0)//If this condition is removed, changed or replaced with anything else, the player's jumps go on forever. Until the button is released, of course.
     {
         isOnGround = 1;
     }
     
 }