Proposal for new YUI.Features

Features.md

New YUI Feature Detection

This is my proposal for revamping the YUI Core Feature detection system.

Problem Space

• 90% of our so-called "Feature Tests" are actually Loader conditional modules.
• Some "free-flowing" tests in DOM modules.
• Not sharable
• Hard to find
• Possible duplicates
• Instance Based
  • Means that each instance re-runs tests that have already been computed
• Not cached
• Not named for easy lookups

Proposed Solution

• Create YUI.Features off the global object
  • YUI.Features.add('name', fn)
  • YUI.Features.has('name') or YUI.Features.supports('name')
  • Store all results in exposed private: YUI.Features._results = {};
  • add will execute, then cache the result. Never executing twice.
  • No tests are executed up front, only on first access.
  • Modules will have access to all the tests because they will be in the seed.
    • Caveat: This may make the seed larger, so care should be taken when creating tests.
• Alias Y.Features to global YUI.Features
• This also requires Y.UA to be moved to YUI.UA
• This may also require refactoring YUI.Env too.
• Refactor all "internal" seed tests (Y.Array/Y.Object) to use new YUI.Features.
• Move all conditionals out of Loader and into a new module (TBD below)
• Teach Loader to use the new tests
  • Maybe adding a feature property to the conditional so the old manual tests still work, UA still works, then feature polls the Feature tests.
• Build step to generate content
  • Tool to list/view current registered modules
  • Shortcut to help create them

Things to Determine

• Where should these things live?
  • Current tests are per module, which I think is wrong. Feature tests should not be module specific.
  • I'm proposing src/features/<tbd>/<testname>.js
• Should we still support the old way for a while?
  • This "may" be a breaking change, that's up for discussion.