"isn’t there a better way to speed up client side loads times without having to mix server side and client side code?"
You're not mixing them, you're using a javascript engine serverside to pre-run your client side js. There is still code separation and your back end doesn't have to be written in JS to accomplish this.
Separately the notion of "isomorphic javascript" if that's what it's called, is not to "mix" client and server code. It's 2 fold: 1 to take down the boundary between client and server code so that there is much re-use and code can just be "marked" as server or client only. 2) So that you can re-use many of your tools like libraries, testing, and language best practices across your whole project.
You're not mixing them, you're using a javascript engine serverside to pre-run your client side js. There is still code separation and your back end doesn't have to be written in JS to accomplish this.
Separately the notion of "isomorphic javascript" if that's what it's called, is not to "mix" client and server code. It's 2 fold: 1 to take down the boundary between client and server code so that there is much re-use and code can just be "marked" as server or client only. 2) So that you can re-use many of your tools like libraries, testing, and language best practices across your whole project.