LocalStorage QuotaExceededError behavior across browser engines

The HTML5 LocalStorage API provides a synchronous key-value store for persisting string data per origin. While most modern browsers implement a storage limit of approximately 5MB, the exact threshold and the resulting behavior when this limit is reached can vary.

When a setItem() operation exceeds the available capacity, the browser is expected to throw a QuotaExceededError. However, the precision of this limit and the consistency of the error trigger across different browser engines remain a point of uncertainty for applications requiring strict storage budget management.

• Is the 5MB limit calculated based on the number of characters or the actual byte size of the UTF-16 strings?
• Do different browser engines handle the QuotaExceededError consistently when the limit is reached during a sequence of multiple small writes versus one large write?