add a $.delay() function

[pmcelhaney]

It would be nice to have a function that simulates lag.

export const GET: HTTPGet = async ($) => {
   // wait 2 seconds;
   await $.delay(2000);
   return $.response[200].json("ok"); 
}

It's a matter of adding a function to the return value of the the endpoint function in src/server/resgistry.ts

         query: castParameters(requestData.query, parameterTypes.query),
+
+        delay: async (milliseconds: number) =>
+          // eslint-disable-next-line promise/avoid-new
+          await new Promise((resolve) => {
+            setTimeout(resolve, milliseconds);
+          }),
       });

For type safety, the new property would need to be added to the RequestData type of the same file.

Extra credit

1. Add a unit test.
2. Add an optional second argument, so that delay(1000, 4000) will create a random delay between 1 and 4 seconds.
3. Make it work even if we forget to put await before $.delay(...).
4. Add an optional third argument, which is a probability distribution function.

[pmcelhaney]

Should we also add a --delay argument to the CLI that would apply to all endpoints?

In my experience it tends to be a couple of specific endpoints that are notably slow. But I'm sure someone's going to look for a command line argument. Give the people what they want?

[dethell]

I'd say adding it to $ is sufficient rather than delaying the entire thing. If we want to test an overall delay in the browser we can use the DevTools in Chrome (or whatever) to throttle everything.