Thank you for the opportunity to help you with your question!
Function declaration and function expression should be used case by case.
The perfomance difference is that:
Even though they seem similar, the
difference lies in how the browser loads them. Functions declaration loads
before any code is executed while function expressions loads only when the interpreter
reaches that line of code. Thus working together improves performance.
Please let me know if you need any clarification. I'm always happy to answer your questions.