for..in

JavaScript

var array = [3, 4, 7, 9, 10, 13];
var secondArray = [3, 4, 9, 13, 23];
var object = {"cat" : 3, "dog": 10};

function containsTen(toCheck) {
    //Note that x refers to the index of an array, not the actual value itself.
    //This is true when objects are used as well.
    for(var x in toCheck) {
         if(toCheck[x] == 10)
             return true;
    }


    return false;
}