We have provided some solution on the custom button if you need to check more condition. This below code is helpful to Salesforce learner to understand the basic.
For example :-
First if condition satisfies the go to other condition otherwise show the else result. Here i checked first condition if contact is active go to check birthday date and month same as today otherwise show the else result. Click the pop up button it will show the result.
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alert( {!IF(ISPICKVAL( Contact.Active__c , 'Yes'), Successfully Updated, 'NotActive')} ); ===================================================================
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