jump script : 2D

hello everyone,

I am trying to make my character(Plane gameobject) double jump.. I am developing 2d game and i have animated zombie character running in x-y plane.. My zombie character is not the 3D model..

Script which i have written associated with this zombie character is here :

 public var maxSpeed : float ;
 public var minSpeed : float ;
 public var jump : int = 10;
 public var dJump : int = 7;
 public var isJumping : boolean = false;
 public var isDJumping : boolean = false;
 public var gravity : int = 20;
 
 private var x : float;
 private var y : float;
 private var z : float;
 private var currentSpeed : float;
 private var stop : boolean = false;
 private var velocity : Vector3 = Vector3.zero;
 
 private static var fenceEnemy : int;
 
 function Start () {
     SetPositionandSpeed();
 }
 
 function Update () {
     
     var amttomove : float = currentSpeed * Time.deltaTime;
     //velocity = Vector3 (0, 0, );
     
     if(!stop)
         transform.Translate(Vector3.left * amttomove , Space.World);
         
     if(isJumping)    
     {
         rigidbody.constraints = RigidbodyConstraints.FreezeRotation | RigidbodyConstraints.FreezePositionZ;
         rigidbody.AddForce(Vector3.up * jump);
         isJumping = false;    
     }
     else
     {
         rigidbody.constraints = RigidbodyConstraints.FreezeRotation | RigidbodyConstraints.FreezePositionY | RigidbodyConstraints.FreezePositionZ;
     }
     //rigidbody.velocity.y -= gravity * Time.deltaTime;
 }
 
 function SetPositionandSpeed()
 {
     currentSpeed = Random.Range(minSpeed , maxSpeed);    
     x = 12.00;
     z = -5.00f;
     y = Random.Range(-6.0f , 1.5f);
     transform.position = new Vector3(x , y , z);
 }

Now when i shoot the zombie i want to make double jump kind of effect.. So what can i do ? Have tried above code but could not able to get the result..

Please help me.. Thanks in advance for your support and help..