How to controll parameters in animator using javascript

I am having trouble with setting up the script here. All i want the character to do is when left shift is pressed set "isRunning" parameter to true and the the key is released go back to original state (idle). I tried using hash id but I couldn't get it to work. Pls help me with the script:

 #pragma strict
 
 var anim : Animator;
 var runHash : int = Animator.StringToHash("Run");
 
 
 function Start () 
 {
     anim = GetComponent("Animator");
 }
 
 
 function Update () 
 {
     if(Input.GetKeyDown(KeyCode.LeftShift))
     {
         anim.SetTrigger (runHash);
     }
 }