const regex = /,([^,]*)$/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp(',([^,]*)$', 'gm')
const str = `http://stackoverflow.com/questions/3829483/how-to-replace-last-occurrence-of-characters-in-a-string-using-javascript
DailyStats,jlaer;priatil;uido,DailyStatsAdm
AuditEvents,aorl;atil;le;mran;uido,AuditEventsAdm
`;
const subst = `;$1`;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions