Asynchronous templating

[aalpern]

Tessera currently uses handlebars for expanding templates in items such as the markdown item, and most importantly in queries. Internal to UA (to be released eventually) we integrate that with handlebars helper functions that call clusto to build graphite queries from role-based queries to clusto (to retrieve hostnames).

Because handlebars is synchronous, that means making synchronous HTTP calls, which is no fun (mitigated by in-browser caching, but still...).

Possible approaches to mitigate this:

• Replace the template engine with one that supports both async rendering and async extensions. This also means re-writing portions of dashboard rendering using Promises (also not a bad thing). It also likely means some incompatibilities in the templates (see below), which is not ideal but probably acceptable.
• Keep handlebars, but add an async data gathering phase, so we don't need to make async calls within template helpers. This is attractive from an MVC standpoint, but would really need a much more sophisticated editor (which is probably much more expensive to write, in terms of effort).

Async Template Engines

• nunjucks - A Deep Dive into Asynchronous Templating is a great writeup.
• dustjs
• marko

[aalpern]

Oh, this is interesting - https://github.com/nknapp/promised-handlebars