re: A New Coding Style for Switch Statements in JavaScript/TypeScript VIEW POST

re: Why not let entry; at the top of the switch block? If you're trying to set a variable from multiple place, it's not a constant. Adding a scope, r...

In this example I'm not trying to set one variable from multiple places. Rather, I'm trying to set two different variables once each that never change. They actually are constants.

Each variable also has a different type in TypeScript too. There is a base class between them, but explicitly specifying the base class on the let and then casting in the function calls adds extra scaffolding that I don't think is necessary and want to avoid.

I'm not worried about adding another stack frame TBH. Once upon a time there was a performance cost to extra stack frames (and to function calls, try/catch/etc.), but V8 has been optimized enough these days that this only matters for extremely hot paths. And if this were a hot path, I'd write it pretty differently anyways, after taking the time to measure it and prove it's a hot path in need of optimization.


Yeah, a place I've done this is in writing switch statements in reducers. The extra scope also closes over any intermediate values you have so you don't have to coordinate variable names between blocks. I do this routinely for all switch statements all the time for this reason. The semantics are more useful and obvious with the braces.

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