[REQUEST] Prime by promise

[WillSquire]

The issue is with race conditions occurring during fast create and subsequent delete mutations. In short, delete requests can happen much faster than create requests. In long:

• Create request is received by server
• Server sends create request to update state
• Delete request is received by server
• Delete request checks the existence of the entity, but it's not been created yet

It seems like a nice solution would be to prime Dataloader's cache with a Promise so that the delete request hits this and can await the response of the created entity. I.e. either returning the entity, or undefined. I tried doing this, but the typings expect the resolved value rather than a Promise.

As an alternative, the issue has been somewhat mitigated by client debouncing. It's not fool proof however, and still happens.

[LinusU]

It seems like this is already supported in the code base:

dataloader/src/index.js

Lines 196 to 198 in 249b2b9

	} else {
	promise = Promise.resolve(value);
	}

But the typings doesn't allow calling .prime() with a Promise<V>