How to skip transform javascript code?

[hardfist]

we want to use esbuild as our build tools(which is super fast), But because our target is not browser and node( an embed Javascript runtime), which transform may break code , so I want to know is there any way to disable transform Javascript code when bundle, thanks。

[evanw]

It's not currently possible to set the platform to something other than the browser or node. Can you say more about your use case? Which of esbuild's transforms are breaking your code, and how?

[hardfist]

our build tools use two different javascript languages(for different purpose), one of which supports a subset of es3(JS-A), which most transform tools doesn't support, but we support esm by using rollup for now(because rollup doesn't do any transform by default, which meets our needs),and another js language(supports es5+,JS-B) use esbuild as our build tools, so we want also want to use esbuild instead of rollup to build the JS-A,but the transform result may break the code。

[evanw]

You can now specify --platform=neutral to disable esbuild's defaults. There is more information here: https://esbuild.github.io/api/#platform.

[hardfist]

https://esbuild.github.io/api/#platform

It seems that even though I set platform neutral, It still do some transform(like transform let to var)

[SergeiMinaev]

Same here. I want to keep consts for example. Is there any way to bundle files without transpilation? I'd like to keep the code as is.

[evanw]

I want to keep consts for example.

Why do you want to do this? Is it just for aesthetics? Whenever const is transformed to something else, esbuild makes assigning to a const symbol a build error so it should not be possible to bundle code that assigns to const and have it work at run time (in case that's what you are worried about).

It is intentionally not possible to keep top-level const symbols as const during bundling because some upcoming bundling features will require removing top-level const symbols to allow for lazy initialization of modules. In addition, changing top-level const and let to var improves the performance of your code. The const and let features introduce additional overhead compared to var because of checks for something called the "temporal dead zone." This is especially problematic for bundling because bundling creates a single extremely large top-level scope with lots of variables, and certain JavaScript VMs have a huge performance penalty (e.g. >5 additional seconds of initialization time) in this case if you use const and let instead of var.

[SergeiMinaev]

Is it just for aesthetics?

Yeah, it looks like this.

Whenever const is transformed to something else, esbuild makes assigning to a const symbol a build error so it should not be possible to bundle code that assigns to const and have it work at run time (in case that's what you are worried about).

Ok I got it.

This is especially problematic for bundling because bundling creates a single extremely large top-level scope with lots of variables, and certain JavaScript VMs have a huge performance penalty (e.g. >5 additional seconds of initialization time) in this case if you use const and let instead of var.

Wow, this is interesting. I should rethink the priorities. Thanks!

[hardfist]

my case is very special, our javascript vm implementation does not support var,but support let, when esbuild transform let to var, it breaks our code

[evanw]

my case is very special, our javascript vm implementation does not support var,but support let, when esbuild transform let to var, it breaks our code

That is interesting. However, I do not intend for esbuild to include logic for handling JavaScript language subsets like this. Various parts of esbuild's internals may produce var when bundling even independent of what your code looks like. This is because var is an older language feature than let, and it is assumed that older language features are safer to use than newer language features.

[hardfist]

so esbuild's tranformer function is not opt-in but bound to it's other functionality?

[hardfist]

@evanw , Except let | var | const things, can other transformer features be opt-out ? esbuild plugin is so much elegant than rollup when deal with virtual module, This is the last thing stop I migrate from rollup.

[therealparmesh]

We use SWC quite a bit, but we also love the bundling functionality that esbuild provides over Webpack. If we could optionally skip the transform step for esbuild given that we use an esbuild SWC plugin, that'd be a perfect setup for us. Is there any chance that such a proposed change would be accepted?