Have you not looked at benchmarks? It's one of, if not the fastest interpreted language. V8 is baked into Electron (and Node), which means Electron can also take advantage of this speed.
High memory usage I'll give you, but calling it a slow language is very misguided.
I do use compiled languages, but there's many different tools for the job. Interpreted languages offer a number of features over compiled, and that makes it an attractive option in many situations.
In the case of JS, the biggest draw is probably platform portability and the amount of existing code to utilize. That and speed, as already mentioned.
Yeah, that's why you use JS and Electron, right?