repeat object spawn

How do I make a prefab spawn repeatedly? Here's my prefab spawn script

var evilsphere : Transform;

function Start () {

yield WaitForSeconds (1); Instantiate (evilsphere, transform.position,
transform.rotation); 

} 

Use InvokeRepeating:

var evilsphere : Transform;
var waitTime = 1.0;

function Start () {
   InvokeRepeating ("Spawn", waitTime, waitTime);
}

function Spawn () {
   Instantiate (evilsphere, transform.position, transform.rotation);
}

This previous question answers your question:

http://answers.unity3d.com/questions/14913/programming-help-with-instantiate/14934#14934

The idea to use yield is correct. But you will have to use this in a Coroutine to work.

var evilsphere : GameObject;

function Start () {
  SpawnRoutine();
}

function SpawnRoutine () {
  while(true) {
    Instantiate (evilsphere, transform.position, transform.rotation);
    yield WaitForSeconds(1);
  } 
}