keep-names may cause some errors

[alienzhou]

I found that using KeepNames will add a def function (__name) at the begin. When the module uses .toString() to get a function's source code and use it to execute (new Function / new Worker). The def function will be out of the scope.

An original module below

function main(a, b) {
    function log(a1, b1) {
        console.log(a1, b1);
    }
    log(a, b);
}

const code = `(${main.toString()})(1, 2)`;
new Worker(URL.createObjectURL(new Blob([code])));

will be transformed to

var __defProp = Object.defineProperty;
var __name = (target, value) => __defProp(target, "name", { value, configurable: true });
function main(a, b) {
  function log(a1, b1) {
    console.log(a1, b1);
  }
  __name(log, "log");
  log(a, b);
}
__name(main, "main");
const code = `(${main.toString()})(1, 2)`;
new Worker(URL.createObjectURL(new Blob([code])));

Now main needs __name when it is executed. However there no definition in main.toString().

---

canvas-confetti is a real package with the edge case.

After enabling useWorker:

confetti1.create(document.getElementById('ca1'), {
  resize: true,
  useWorker: true,
});

Here's a simple demo: https://gist.github.com/alienzhou/75e1f1a4c7fdbbf7cabce4469688df1b#file-esm-sh-simple-example-html
(works well in v82 and is broken in v83)

It's more like a problem of esbuild. Maybe adding an option for users?