WP-API JS Client: Add a helper to get model or collection by route

[adamsilverstein]

In the process of adding page/custom post type support to Gutenberg, the need arose to identify the models based on their route - the code passes the route from PHP to JavaScript, and the JavaScript needs to know which model to use. See ​this pull requst for additional details.

We should add helpers to the client to easily find a model or collection based on its route, something like getModelByRoute and getCollectionByRoute - each would search thru the constructed models/collections and return the matching object, or false if none was found. We should also add unit tests to verify the functions work as expected.

[rcutmore]

Add helper methods and unit tests

[rcutmore]

Hi @adamsilverstein

I added 41111.diff to add these helper methods as well as the associated unit tests. Let me know if this is on the right track or if I'm missing anything. I wasn't sure exactly where the helper methods should be added.

[adamsilverstein]

@rcutmore looks good at first glance, I will take a closer look soon. Thanks for your work here!

[adamsilverstein]

@rcutmore - nice work here!

In 41111.2.diff​ I moved the code up a bit into the utility section, ultimately we will probably split this file back up so wanted to group the functions with the other helpers. Also, I clarified the return value would be undefined if not matching item is found and I switched out _.first( _.filter(... for _.find(... which should also return the first item matching the predicate. This makes the code a little more legible and all the unit tests continued to pass.

[adamsilverstein]

41111.3.diff​

• remove some trailing commas to make jshint happy

Question: do we still need these tests if we no longer support older versions of IE?

cc: @netweb 

[adamsilverstein]

In 41334:

WP-API JS Client: Add helpers to get a model or collection by route.

Add two new helper functions, wp.api.getModelByRoute and wp.api.getCollectionByRoute. Passed a route, they return the matching model or collection, or undefined if none is found.

Also adds tests to verify these functions work as expected.

Props rcutmore.
Fixes #41111.