Multiple calls to new Date() should return a fixed time

[ItalyPaleAle]

In a "real" Workers environment, creating new Date objects or returning the current time always return the same value for every call while performing a request. This applies to the new Date() constructor, methods like Date.now(), etc: they return the current time (technically, the time the request was received at), and then subsequent calls return the same value. (Documentation)

In Miniflare, this behavior is not observed. Instead, multiple calls to methods like Date.now() return different values.

Ideally, Miniflare should mirror the behavior of the "real" Workers environment.

[mrbbot]

Hey! 👋 Thanks for raising this.

Initially, I made the decision not to implement this as spectre attacks aren't as big of a deal for local development. Additionally, I thought it might be useful to allow users to measure execution times for different parts of their workers during development.

However, you're right, this is a behaviour mismatch. Now that we have a per request context, it should be possible to implement this. I seem to remember that the returned time advanced on any async I/O, but I can't seem to find the docs for it anymore.

If people want to measure execution times, they should be able to use the profiling provided by the Node.js Inspector.

[ItalyPaleAle]

As I think a bit more about this, and applying Hyrum's law, I wonder if the old behavior (having Date always represent the current time) should be kept available for example using a flag? I suspect that there will be at least some people who depend on that behavior, maybe for their unit tests.