Can't use for-in statement in strict javascript.

Hello, I'm writing a game using strict javascript in unity3d (#pragma strict), I wrote the code below in the Start function, but it reports error

#pragma strict

function Start () {

 // Make all animations in this character play at half speed
 for ( var state : AnimationState in animation ) {
     state.speed = 0.5;
 }

}

The compile error is:

BCE0022: Cannot convert 'Object' to 'UnityEngine.AnimationState'.

What should I do?