implement lowering for using
and await using
#3192
Merged
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TypeScript 5.2 (due to be released in August of 2023) will introduce
using
declarations, which will allow you to automatically dispose of the declared resources when leaving the current scope. You can read the TypeScript PR for this feature for more information. This PR adds support for transforming this syntax to target environments without support forusing
declarations (which is currently all targets other thanesnext
). Here's an example (helper functions are omitted):The injected helper functions ensure that the method called
Symbol.dispose
is called onnew Foo
when control exits the scope. Note that as with all new JavaScript APIs, you'll need to polyfillSymbol.dispose
if it's not present before you use it. This is not something that esbuild does for you because esbuild only handles syntax, not APIs. Polyfilling it can be done with something like this:This feature also introduces
await using
declarations which are likeusing
declarations but they callawait
on the disposal method (not on the initializer). Here's an example (helper functions are omitted):The injected helper functions ensure that the method called
Symbol.asyncDispose
is called onnew Foo
when control exits the scope, and that the returned promise is awaited. Similarly toSymbol.dispose
, you'll also need to polyfillSymbol.asyncDispose
before you use it.Fixes #3191