Custom Button "OnClick JavaScript" stopped working

As an addendum to Ilya's clever response, I thing a decent approach to getting lucidity in the in the Java event that assertion is to eliminate a portion of the limiting rationale and assess it earlier.
What I'd typically do if my on the off chance that assertion was getting hard to comprehend is either utilize a capability to assess the articulation - ie:
if( isCreditedInvoice())
Or on the other hand (more probable for this situation):
var isInvoice = "{!Animal__c.RecordType}" == "2 - Invoice" ? valid : bogus;
var isCredited = "{!Animal__c.Invoice_Status__c}" == "Credited" ? valid : bogus;
Then you can compose the wonderful clear assertion:
on the off chance that (isInvoice && isCredited){
//do stuff
}
What's more, obviously, you could attempt this choice as well:
var recordType = "{!Animal__c.RecordType}";
var invoiceStatus = "{!Animal__c.Invoice_Status__c}";
You proclamation will seem to be this:
if (recordType == "2 - Invoice" && invoiceStatus == "Credited"){
//do stuff
}
At any rate, this is just trying to say that assuming you dynamic away a portion of the stray pieces, you can make your occupation more straightforward.