You can't do it as simply as you stated, but you could do something like this:
var arr:Array = new Array(1,3,5,7,6,8);
var testarray:Array = new Array(3,6,8);
var found:Boolean = true;
var j:String;
for(j in testarray){
(checkIt(testarray[j]));
}
function checkIt(obj:Object):void{
if(arr.indexOf(obj) < 0){
found = false;
}
}
trace("found all elements = "+found);