JavaScripting InDesign

I've gone off attaching methods to core JavaScript classes. This week, I've had two scripts fail dismally because of it, so even though the format of working with:

Object.prototype.isInArray = function(myArray){
  for (var i=0; myArray.length > i; i++) {
    if(myArray[i] == this){
      return true;
    }
  }
  return false;
}

is so convenient

if (myObj.isInArray(myArray)) {

or with:

Array.prototype.contains = function(myString){
  for (var i=0; this.length > i; i++) {
    if(myString == this[i]){
      return true;
    }
  }
  return false;
}

if (myArray.contains(myObj)) {

They can really backfire and slap you in the face if you're doing work that involves creating objects or arrays and examining their contents. So, I'm back to the prosaic but safe:

function arrayContains(anArray, anItem) {
  for (var i = 0; anArray.length > i; i++) {
    if (anItem == anArray[i]) return true;
  }
  return false;
}

if (arrayContains(myArray, myObj)) {

Which most people would have been using all along anyway.