Dynamic import breaks object identity

[heypiotr]

Minimal repro: esm-shims-1.3-issue.zip. Downgrading to 1.2 fixes the issue.

Situation: I've got modules "a.js" and "b.js", import-mapped under "a" and "b" respectively. Both of these modules import an object from "./common.js", and expose it on window.common_a and window.common_b (just for debugging).

If I do:

<script type="module">
import "a";
await import("b");
console.log(window.common_a === window.common_b);
</script>

... then in Safari and Firefox (polyfilled import maps), the console.log expression evalautes to false, i.e., the supposedly shared common object actually ends up being different in a and b.

In Chrome, it works as expected:

In a real situation, "a" is ReactDOM, "b" is a React component, and "common" is React, which means trouble 😄

[guybedford]

Thanks for the clear replication, fix in #220.