Not sure what performance first means, but you shouldn't optimize first. Its better to optimize later so that you can profile the performance of your overall system and only optimize what matters.
This isn't really true. Even at the broadest design level, there are many ways to do one thing, and some are faster than others.
IMHO it doesn't really matter in the web frontend context, which is what this thread is about (you can always easily go back to the drawing board if performance becomes a real problem). I will grant you that if you need to build a video streaming service for example, it may be worth building certain components of your backend in C++ right out of the gate.
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