It’s not fundamentally impossible to build fast apps in JS. It’s just not possible to do if you don’t do the legwork of writing code that the compiler will optimize for you. It’s not easy, and it’s not natural in a lot of cases, but saying it is fundamentally impossible goes too far: people build high performance applications like games in JS.
For example, you are worried about value types but under the hood the JIT compiler will actually generate efficient representations that are passed by value if you do not mess things up for it. Modern JS compilers are extremely sophisticated.
For returning values without an allocation, you’d create such a “struct” and then use a memory pool. It would still be heap allocated I believe but not totally sure. People who know more than I do could probably tell you a better method to return multiple values from a function efficiently.
> people build high performance applications like games in JS
Yes, and in my experience this kind of applications (and the browser in general) are one of the only things these days that still push me to upgrade my hardware to have better CPUs and more RAM, as it's perfectly sufficient as is for pretty much everything else I do.
You can’t tell from the outside if you are running a well engineered JS app that would have been fast in another platform, or a non-optimized JS app. My point was that it’s not fundamentally impossible to write fast enough JS code for a game, even though you may come across many slow JS apps regularly. (Not surprising, given the wide distribution and low barrier to entry of the web.)
Yes, you can operate strictly on typed arrays and essentially implement something alike a virtual machine inside your JS code to make it handle memory efficiently, so you're right - it's not "fundamentally impossible", but are you still really writing JavaScript at that point? :P
For example, you are worried about value types but under the hood the JIT compiler will actually generate efficient representations that are passed by value if you do not mess things up for it. Modern JS compilers are extremely sophisticated.
For returning values without an allocation, you’d create such a “struct” and then use a memory pool. It would still be heap allocated I believe but not totally sure. People who know more than I do could probably tell you a better method to return multiple values from a function efficiently.