multiple instantiate object script help

im making a block based building game and im making it so when you press 1 and left click it places block 1, press 2 block2 etc. so i dont know how to script it. heres my script.

CODE:

 var blockLayer : LayerMask = 1;
 var range : float = Mathf.Infinity;
 var hit : RaycastHit;
 var block1 : Transform;
 var block2 : Transform;
 var block3 : Transform;
 var block4 : Transform;
 var whichblock = 1;
 
 function Block4 ()
 {
     if (Input.GetKeyDown(4))
         var whichblock = 4;
 }
 
 function Block3 ()
 {
     if (Input.GetKeyDown(3))
         var whichblock = 3;
 }
 
 function Block2 ()
 {
     if (Input.GetKeyDown(2))
         var whichblock = 2;
 }
 
 function Block1 ()
 {
     if (Input.GetKeyDown(1))
         var whichblock = 1;
 }
 
 function Update () {
         if (Input.GetMouseButtonDown(0))
         {
         if (whichblock) == 1;
         Build1(); 
         if (whichblock) == 2;
         Build2();
         if (whichblock) == 3;
         Build3();
         if (whichblock) == 4;
         Build4();
         }
     
     if (Input.GetMouseButtonDown(1))
         Erase();
 }
 
 function Build1() {
     if (HitBlock()) {
         Instantiate (block1);
         block1.transform.position = hit.transform.position + hit.normal;
         }
     }
     
 function Build2() {
     if (HitBlock()) {
         Instantiate (block2);
         block2.transform.position = hit.transform.position + hit.normal;
         }
     }
 
 function Build3() {
     if (HitBlock()) {
         Instantiate (block3);
         block3.transform.position = hit.transform.position + hit.normal;
         }
     }
     
 function Build4() {
     if (HitBlock()) {
         Instantiate (block4);
         block4.transform.position = hit.transform.position + hit.normal;
         }
     }
 
 
 function Erase() {
     if (HitBlock())
         Destroy(hit.transform.gameObject);
 }
 
 function HitBlock() : boolean {
     return Physics.Raycast(transform.position, transform.forward, hit, range, blockLayer);
 }