As described here: https://github.com/WebAssembly/design/blob/master/JS.md#structured-clone-of-a-webassemblymodule
> Structured Clone of a WebAssembly.Module
> A WebAssembly.Module is a cloneable object† which means it can be cloned between windows/workers and also stored/retrieved into/from an IDBObjectStore‡. The semantics of a structured clone is as-if the binary source, from which the WebAssembly.Module was compiled, were cloned and recompiled into the target realm. Engines should attempt to share/reuse internal compiled code when performing a structured clone although, in corner cases like CPU upgrade or browser update, this may not be possible and full recompilation may be necessary.
> Given the above engine optimizations, structured cloning provides developers explicit control over both compiled-code caching and cross-window/worker code sharing.
This can give a great push to startup time as mentioned in
For example startup time of webassembly app which takes 2+ sec on Safari 11 on a latest fast mac machine gets loaded from indexeddb in less than 200 milliseconds.
*** Bug 178163 has been marked as a duplicate of this bug. ***
This could be closed per https://github.com/WebAssembly/spec/issues/821
IndexedDB should be replaced by Caching API