How to implement Aggro into a AI script (Js)

Hey guys how would i go about adding an aggro radius in this script, im quite confused at the moment

 var target : Transform; //the enemy's target
 var moveSpeed = 3; //move speed
 var rotationSpeed = 3; //speed of turning
 var attackRange = 3; // distance within which to attack
 var chaseRange = 10; // distance within which to start chasing
 var giveUpRange = 20; // distance beyond which AI gives up
 var attackRepeatTime : float = 1.5; // delay between attacks when within range
 var anim : GameObject;
 var maximumHitPoints = 5.0;
 var hitPoints = 5.0;
 var attack : AudioClip;
 private var chasing = false;
 private var attackTime : float;
 var checkRay : boolean = false;
 var idleAnim : String = "idle";
 var walkAnim : String = "walk";
 var attackAnim : String = "attack"; 
 var dontComeCloserRange : int = 4;
 
 private var myTransform : Transform; //current transform data of this enemy
 
 function Awake(){
     myTransform = transform; //cache transform data for easy access/preformance
     anim.animation.wrapMode = WrapMode.Loop;
     anim.animation[attackAnim].wrapMode = WrapMode.Once;
     anim.animation[attackAnim].layer = 2;
     anim.animation.Stop();
 }
 
 function Start(){
     target = GameObject.FindWithTag("Player").transform;
 }
 
 function Update () {
     // check distance to target every frame:
     var distance = (target.position - myTransform.position).magnitude;
     
     if (distance < dontComeCloserRange){
             moveSpeed = 0;
             
             anim.animation[idleAnim].speed = .4;
             anim.animation.CrossFade(idleAnim);
         }else{
             moveSpeed = Random.Range(4, 6);
             anim.animation.CrossFade(walkAnim);
         }
     
     if (chasing) {    
         //move towards the player
         myTransform.position += myTransform.forward * moveSpeed * Time.deltaTime;
         
 
         //rotate to look at the player
         myTransform.rotation = Quaternion.Slerp(myTransform.rotation, Quaternion.LookRotation(target.position - myTransform.position), rotationSpeed*Time.deltaTime);
         transform.eulerAngles = Vector3(0, transform.eulerAngles.y, 0); 
 
         // give up, if too far away from target:
         if (distance > giveUpRange) {
             chasing = false;
         }
 
         // attack, if close enough, and if time is OK:
         if (distance < attackRange && Time.time > attackTime) {
             anim.animation[attackAnim].speed = 2.0;
             anim.animation.CrossFade(attackAnim);
             target.SendMessage( "PlayerDamage", maximumHitPoints);
             attackTime = Time.time + attackRepeatTime;
             audio.PlayOneShot(attack, 1.0 / audio.volume);
         }
 
     } else {
         // not currently chasing.
         anim.animation[idleAnim].speed = .4;
         anim.animation.CrossFade(idleAnim);
         // start chasing if target comes close enough
         if (distance < chaseRange) {
             chasing = true;
         }
     }
 }
 
 
 function OnDrawGizmosSelected (){
     Gizmos.color = Color.yellow;
     Gizmos.DrawWireSphere (transform.position, attackRange);
     Gizmos.color = Color.red;
     Gizmos.DrawWireSphere (transform.position, chaseRange);
 }