2d move to point script help

im trying to create a script for 2d gsme and want an enemy to move to point and stop but move back if knocked around now i have a script i got off here(thanks) with some edting but all i need is if the Vector3 Y value of is to hight the enemy stops

var y : float ;
if (transform.position != Vector3(100,-77.48621,79.44936));
if (transform.position <= Vector3.y(-77.48621));
function Start () {

 var pointA = transform.position;  
 var pointB = Vector3(100,-77.48621,79.44936);  
 while (true) {
     yield MoveObject(transform, pointA, pointB, 3.0);  
     yield MoveObject(transform, pointB, pointB, 3.0);  
 }  

}

function MoveObject (thisTransform : Transform, startPos : Vector3, endPos : Vector3, time : float) {
var i = 0.0; var rate = 1.0/time; while (i < 1.0) { i += Time.deltaTime * rate;
thisTransform.position = Vector3.Lerp(startPos, endPos, i);
yield;
}
} thanks in advance