How can top-level await affect an ES module graph and application startup?

Direct answer

Top-level await makes module evaluation asynchronous; importers that depend on that module must wait for the relevant asynchronous dependency chain, which can delay execution and make cycles more difficult to reason about.

With top-level await, a module can pause its evaluation while an asynchronous operation completes. Modules that depend on it cannot simply continue as though the dependency had synchronously finished initializing. The async status can therefore propagate through dependent parts of the module graph.

This is useful for environment initialization or resources that truly must exist before dependent modules execute, but placing network requests or optional setup at top level can turn module loading into a hidden startup dependency. It can also make cyclic graphs substantially harder to reason about.

Prefer top-level await when asynchronous initialization is genuinely part of the module contract.
For optional or user-triggered work, an explicit async initialization function is often easier to control and test.
Dynamic import() can sometimes isolate asynchronous loading instead of forcing the initial dependency graph to wait.