What's wrong with this JavaScript BigInt mixing with Number?

What's wrong with this JavaScript BigInt mixing with Number in a calculator. The JavaScript code adds BigInt and Number. In JavaScript this throws and crashes the app.

#whatswrongwiththisjavascriptcode #javascriptbug #javascriptproductionbug #javascriptdebugging #javascriptbackend #javascriptcodereview #javascriptsecurity #javascriptperformance #javascriptreliability #javascriptapi #jav...

https://www.youtube.com/watch?v=Ldda7gXnons