App Placeholders

[brianbaker]

Porting a proposed v2 enhancement to v1. Here are the updates so far:

• fixed duplicate sourcemap call in Gruntfile
• added F2.loadPlaceholders
• fixed comments surrounding the CSS classes that are applied to apps
  when rendering
• fixed a bug where the wrong CSS classes were being applied with the
  default AppHandlers
• added logic to allow placeholder apps to bypass AppHandlers
• added autoload logic for placeholders
• added a basic container to demonstrate placeholder functionality
• added unit tests surrounding placeholders
• fixed a bug in the example containers where the proper CSS classes
  were not being applied
• fixed failing unit test related to F2.removeApp() that appears unrelated to these updates

Remaining To Do: See #142

• When using the "autoload" there is no way to customize the ContainerConfig. Should there be? See When using "autoload" there is no way to customize the ContainerConfig #186
• Currently an ID selector is used for determining "autoload". Should a class or attribute be used instead?
• classes and attributes are now supported
• Currently the entire document is scoured to find apps with a data-f2-appid attribute. Should the search be narrowed to elements with an "autoload" attribute?
• only elements with an "autoload" (id/class/attibute) will be processed
• Currently only the appId, manifestUrl and context properties of the AppConfig are pulled from the placeholders. Should more properties be pulled? See Autoload placeholder configuration attributes #187
• Update the docs.openf2.org to explain the feature See Add autoload documentation to Container spec #188

[ilinkuo]

Could you explain what is meant by placeholders? I took a look at the pull request but couldn't understand the intent of the code.

[brianbaker]

Check out the basic example container for example usage. Basically, F2 is just going to search the DOM for elements with data-f2-appid and grab the attributes of that element to build up an AppConfig and then register the app. The app will be rendered inside of that "placeholder" element.

[ilinkuo]

I get it now. Thanks for the explanation. I think of this as a declarative style vs. the older imperative style.