iTween - I need help with "onstart"

I want to animate gameobjects from the lists. I need to switch their visibility on with the “onstart”, but can not get the below script working:

import System.Collections.Generic;

var goList: List.<GameObject>;
var del2: float;
var t00: float;

for (var i=0; i<n; i++) {
//incorrtect
iTween.MoveBy(goList_,{"z":-5, "delay":t00 + i2*del2,"onstart":"activate", "onstarttarget":"gameObject","onstartparams":"i"});_

//correct
iTween.MoveBy(goList_,{“z”:-5, “delay”:t00 + i2*del2,“onstart”:“activate”, “onstarttarget”:gameObject,“onstartparams”:i});_

* }*

function activate (k) {
* goList[k].renderer.enabled = true;*
}
Actually I am getting a runtime error:
InvalidCastException: Cannot cast from source type to destination type.

Try something like this:

function activate (k:int) {
    goList[k].renderer.enabled = true;
}

And also lose the quotes around the “i” and “gameObject” in your MoveTo command. No guaranteees, though. My experience with UnityScript is limited, because it is too weird a language.