Is there a reason Web doesn't support fence/sync calls?

[BStringhamVRSK]

I just posted this bug report that relates to this discussion: #7395
I'm trying to resolve some CPU/GPU synchronization problems we see only on Web. On other platforms, we use fences to manage synchronization, but the JavaScript/TypeScript interface is missing these calls:

• Engine::createFence()
• Engine::destroy(fence)
• Fence::Wait()
• Fence::WaitAndDestroy()

I'm wondering if this is an oversight, or if web has a different architectural reason?
Maybe the CPU and GPU are already forced to be in lock-step with each other in Web? That would cause a lot of wasted CPU and GPU cycles.

The kinds of problems we see are flickering or missing geometry when objects are modified. This looks like a sync issue where the CPU has modified/removed data from an object that is still in the in-flight command buffer. Without fences, this is pretty tough to manage.