async view helpers?

[der-On]

I know that the partial() view helpers works async, by inserting a placeholder.

Is it possible to create own async view helpers working with the same method?

If not what would be the best place to include such kind of feature?

Possible API:

Using functions: if helper methods returns a function, execute this function right after rendering and pass it a callback function as single argument. the callback should get an error as first and the result of the async helper as second argument:

    function asyncHelper() {
      return function(whenDone) {
        // do your async stuff
        whenDone(null, 'this will get insert'); // <- pass an Error instead of null if an error occured
      }; 
    }

Using promises: if the helper method returns a promise, use its resolve() to replace the placeholder content and the catch() to catch helper errors:

    function promiseHelper() {
      return new Promise(function (resolve, reject) {
        // do async stuff
        resolve('this will get insert'); // <- use catch(Error) to pass an error
      });
    }

Using a wrapping build-in async helper: Geddy will include a build-in async view helper. This helper will do almost the same as the existing partial helper and needs either a promise or function as in the upper cases passed as argument. Template code could then look like this:

<%- async(asyncHelper()) %>

or with promise

<%- async(promiseHelper()) %>

The benefits of this are that we could be able to pass options to the helper that would for example trigger caching of the async result.

[der-On]

Work has started in the async-view-helpers branch.

I just tested this in a geddy app and it seems to work. However I currently do not know how to write tests for it. I tried going from the partial tests, but I yet don't know how to actually feed the partials with real template strings: https://github.com/geddy/geddy/blob/async-view-helpers/test/templates/async_partial.js#L10

To explain my approach:

I've used the build-in async() approach and simply created a new helper within the existing Partial code: https://github.com/geddy/geddy/blob/async-view-helpers/lib/template/partial.js#L34