JS: explain camel case & ES6 rules (#39)

Author: wfleming

javascript/README.md

@@ -6,6 +6,24 @@ This repo contains an `eslintrc.js` file that should be included (as
 `.eslintrc.js`) in each project. Periodically, a repo's `.eslintrc.js` file
 should be synced with the one here.
 
+### Variable and Function Names
+
+Names of variables and functions should be CamelCased. This may not be
+practical to enforce automatically with ESLint on all projects, since code
+interacting with APIs will frequently need to snake\_case object properties for
+API queries and such. In those cases, only use snake\_case when interacting
+directly with the API, either querying or handling a response. If an API
+response is being transformed into a model-like object, key names should change
+to CamelCase at that boundary. E.g.:
+
+```
+api.getModel("id").then(function(data) {
+  var model = new Model();
+  model.keyName = data.key_name;
+  return model;
+});
+```
+
 ### JQuery
 
 - Prefer `return false` over `event.preventDefault()` when you don't need the
@@ -24,3 +42,18 @@ should be synced with the one here.
     return false;
   });
   ```
+
+### ECMAScript 6
+
+There is an additional set of ESLint rules we use for ES6 code: these are in
+`eslintrc-es6.js`, and can be included into the main `.eslintrc.js` file in ES6
+projects with an `"extends"` directive.
+
+The rules there are mostly self explanatory, with one perhaps requiring an
+explanatory note: `=>` functions are preferred over the `var self = this;`
+pattern, but not in all cases, as there are good reasons *not* to use `=>`
+sometimes.  The `consistent-this` rule makes it feasible to flag these
+non-preferred usages without causing false positives on other cases, though
+this isn't the strictly intended purpose of the rule. This does not mean that
+`=>` should not be used in any other cases, only that whether to use it or not
+in other cases is a judgment call.

javascript/eslintrc-es6.js

@@ -0,0 +1,10 @@
+module.exports = {
+  "rules": {
+    "consistent-this": [2, "prefer-fat-arrow-over-reassigning-this"],
+    "no-const-assign": 2,
+    "no-var": 2,
+    "prefer-const": 2,
+    "prefer-spread": 2,
+    "prefer-template": 2
+  }
+};