I was interested to try Date.now() since this is mentioned as being the only part of the Date implementation that is supported but was surprised to find it always returns 0 for your microquickjs version - your quickjs variant appears to return the current unix time.

Good catch. WebAssembly doesn't have access to the current time unless the JavaScript host provides it through injecting a function, so the WASM build would need to be hooked up specially to support that.