This introduces new methods related to Iterators on Backbone.Collection to mirror those found on Array: `values`, `keys`, `entries`, and `@@iterator`. Each of these methods will return a JavaScript Iterator, which has a `next` method, yielding the models or ids of models contained in the Collection.
The CollectionIterator is careful to use the `at()` and `modelId()` methods on the host collection rather than direct access to the `models` property, which should ensure it is resilient to creative subclassing of Backbone.Collection and future feature addition.
The [`@@iterator`](http://www.ecma-international.org/ecma-262/6.0/#sec-well-known-symbols) method is defined using `Symbol.iterator` if it exists in the JavaScript runtime (modern browsers/node.js) and falls back to the string `"@@iterator"` which was popularized by older versions of Firefox and has become the standard fallback behavior for other third-party libraries. This ensures that Backbone can still be used across all browsers, even with use of these new methods.
Supporting Iterable allows better integration between Backbone and the most recent additions to the JavaScript language, including `for of` loops and data-collection constructor functions, as well as better integration with other third-party libraries that accept Iterables instead of only Arrays.
Fixes#3954
This is only enabled as a warning, since in some cases I think it adds clarity.
I left the "gratuitous parentheses" when they were clarifying nested ternary
operators or clarifying the evaluation order of `&&`s and `||`s.
In an attempt to bring our ESLint rules closer to those in Underscore, I've
started by adding some whitespace rules which don't involve any significantly
opinionated changes.
This pull request replaces the old "jsl" linter with ESLint and enables it as
part of our integration tests.
So far, the only rules it includes are the ones which are both currently
enforced in Underscore AND are already passing in Backbone.
I will follow up with individual pull requests for each rule which will require
changes to the code in an attempt to bring us in sync with Underscore's style.
