Can anyone understand the problem with this script?

This code is meant to be a GUIButton with a jump function for the player which has a rigidbody. The GUIButton shows up but the jump function doesn't respond. Can anyone point out any issues with this script?

This code is in JS(JavaScript/UnityScript)

 var originalWidth = 1600.0;  // define here the original resolution
 var originalHeight = 900.0; // you used to create the GUI contents 
 var PositionX : float = 100;
 var PositionY : float = 100;
 var SizeX : float = 100;
 var SizeY : float = 100;
 var JumpSpeed: float = 100;
 
 private var scale: Vector3;
 
 function Jump () {
         rigidbody.AddForce (Vector3.up *JumpSpeed);
     }
     
 function Update () {
 
     if(GUI.Button(Rect(PositionX,PositionY,SizeX,SizeY), "Jump"))
         Jump ();
 }
 
 function OnGUI () {
     scale.x = Screen.width/originalWidth; // calculate hor scale
     scale.y = Screen.height/originalHeight; // calculate vert scale
     scale.z = 1;
     var svMat = GUI.matrix; // save current matrix
     // substitute matrix - only scale is altered from standard
     GUI.matrix = Matrix4x4.TRS(Vector3.zero, Quaternion.identity, scale); 
  
 
         if(GUI.Button(Rect(PositionX,PositionY,SizeX,SizeY), "Jump"))
         Jump ();
     }

Thank You