This commit adds guidance warning people to avoid lexical declarations
in case/default clauses and enables the corresponding ESLint rule.
http://eslint.org/docs/rules/no-case-declarations.html
We didn't have a section on switch statements yet, so I thought about
starting one. It seemed like it would best fit between section 15
(Comparison Operators & Equality) and section 16 (Blocks), but I didn't
want to mess up all of the following numberings, since people probably
have references to them. I considered adding this near the end to
minimize this effect, but it really seemed to belong near these other
things. I landed on appending it to Section 15 (Comparison Operators &
Equality) and I think it sorta fits there since switch statements are a
related concept.
[eslint] Add comment above `max-len` rule with link to its docs
[eslint] Change tab width for `max-len` rule from 4 to 2
[eslint] Replace double quotes around `max-len` with single quotes
[eslint] Use object form of `max-len` and include all of the options
isMounted is an anti-pattern [0], is not available when using ES6
classes, and is on its way to being officially deprecated.
eslint-plugin-react recently added the react/no-is-mounted rule in
3.12.0 that prevents its use.
[0]: https://facebook.github.io/react/blog/2015/12/16/ismounted-antipattern.html
Finishes #633
All of the other rules in this file are in alphabetical order, but this
one was added by c98990c0f out of order at the end. Keeping these in
alphabetical order will help developers find the rules that they are
looking for.
Enable [arrow-spacing](http://eslint.org/docs/rules/arrow-spacing.html) rule, code with space before/after arrow function's arrow is easier to read.
```js
() => {};
(a) => {};
a => a;
() => {'\n'};
()=> {}; /*error Missing space before =>*/
() =>{}; /*error Missing space after =>*/
(a)=> {}; /*error Missing space before =>*/
(a) =>{}; /*error Missing space after =>*/
a =>a; /*error Missing space after =>*/
a=> a; /*error Missing space before =>*/
()=> {'\n'}; /*error Missing space before =>*/
() =>{'\n'}; /*error Missing space after =>*/
```
