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RULES.md: Add more examples; minor fixes
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nyuszika7h committed Feb 11, 2017
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111 changes: 63 additions & 48 deletions RULES.md
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Expand Up @@ -570,6 +570,7 @@ your code.

```js
eval( "var result = user." + propName ) // ✗ avoid
var result = user[propName] // ✓ ok
```

* **No reassigning exceptions in `catch` clauses.**
Expand Down Expand Up @@ -656,6 +657,14 @@ your code.
case 2:
doSomethingElse()
}

switch (filter) {
case 1:
doSomething()
// fallthrough // ✓ ok
case 2:
doSomethingElse()
}
```

* **No floating decimals.**
Expand Down Expand Up @@ -689,7 +698,8 @@ your code.
eslint: [`no-implied-eval`](http://eslint.org/docs/rules/no-implied-eval)

```js
setTimeout("alert('Hello world')") // ✗ avoid
setTimeout("alert('Hello world')") // ✗ avoid
setTimeout(function () { alert('Hello world') }) // ✓ ok
```

* **No function declarations in nested blocks.**
Expand All @@ -716,7 +726,7 @@ your code.
eslint: [`no-irregular-whitespace`](http://eslint.org/docs/rules/no-irregular-whitespace)

```js
function myFunc() /*<NBSP>*/{} // ✗ avoid
function myFunc () /*<NBSP>*/{} // ✗ avoid
```

* **No using `__iterator__`.**
Expand Down Expand Up @@ -761,7 +771,7 @@ your code.
}

function myFunc () {
myOtherFunc() // ✓ ok
myOtherFunc() // ✓ ok
}
```

Expand Down Expand Up @@ -897,6 +907,8 @@ your code.

```js
const regexp = /test value/ // ✗ avoid

const regexp = /test {3}value/ // ✓ ok
const regexp = /test value/ // ✓ ok
```

Expand Down Expand Up @@ -1128,6 +1140,7 @@ your code.
}

const user = { name: 'Jane Doe', age: 30, username: 'jdoe86' } // ✓ ok

const user = {
name: 'Jane Doe',
age: 30,
Expand Down Expand Up @@ -1160,7 +1173,7 @@ your code.
fn(...args) // ✓ ok
```

* **Semicolon's must have a space after and no space before.**
* **Semicolons must have a space after and no space before.**

eslint: [`semi-spacing`](http://eslint.org/docs/rules/semi-spacing)

Expand All @@ -1178,7 +1191,7 @@ your code.
if (admin) {...} // ✓ ok
```

* **No spaces inside parens.**
* **No spaces inside parentheses.**

eslint: [`space-in-parens`](http://eslint.org/docs/rules/space-in-parens)

Expand All @@ -1193,7 +1206,7 @@ your code.

```js
typeof!admin // ✗ avoid
typof !admin // ✓ ok
typeof !admin // ✓ ok
```

* **Use spaces inside comments.**
Expand All @@ -1203,6 +1216,9 @@ your code.
```js
//comment // ✗ avoid
// comment // ✓ ok

/*comment*/ // ✗ avoid
/* comment */ // ✓ ok
```

* **No spacing in template strings.**
Expand All @@ -1223,7 +1239,7 @@ your code.
if (isNaN(price)) { } // ✓ ok
```

* **`typeof` must be compared to valid string.**
* **`typeof` must be compared to a valid string.**

eslint: [`valid-typeof`](http://eslint.org/docs/rules/valid-typeof)

Expand All @@ -1232,14 +1248,15 @@ your code.
typeof name === 'undefined' // ✓ ok
```

* **Immediately Invoked Function Expressions (IFFE's) must be wrapped.**
* **Immediately Invoked Function Expressions (IIFEs) must be wrapped.**

eslint: [`wrap-iife`](http://eslint.org/docs/rules/wrap-iife)

```js
const getName = function () { }() // ✗ avoid

const getName = (function () { }) // ✓ ok
const getName = (function () { }()) // ✓ ok
const getName = (function () { })() // ✓ ok
```

* **The `*` in `yield*`expressions must have a space before and after.**
Expand Down Expand Up @@ -1314,7 +1331,7 @@ your code.
;[1, 2, 3].forEach(bar)
```

This is much preferred:
This is strongly preferred:

```js
var nums = [1, 2, 3]
Expand All @@ -1337,44 +1354,42 @@ in JavaScript).

##### Excerpt from *["An Open Letter to JavaScript Leaders Regarding Semicolons"][1]*:

[Relying on automatic semicolon insertion] is quite safe, and perfectly valid JS that every browser understands. Closure compiler, yuicompressor, packer, and jsmin all can properly minify it. There is no performance impact anywhere.

I am sorry that, instead of educating you, the leaders in this language community have given you lies and fear. That was shameful. I recommend learning how statements in JS are actually terminated (and in which cases they are not terminated), so that you can write code that you find beautiful.

In general, `\n` ends a statement unless:
1. The statement has an unclosed paren, array literal, or object literal or ends in some
other way that is not a valid way to end a statement. (For instance, ending with `.`
or `,`.)
2. The line is `--` or `++` (in which case it will decrement/increment the next token.)
3. It is a `for()`, `while()`, `do`, `if()`, or `else`, and there is no `{`
4. The next line starts with `[`, `(`, `+`, `*`, `/`, `-`, `,`, `.`, or some other
binary operator that can only be found between two tokens in a single expression.

The first is pretty obvious. Even JSLint is ok with `\n` chars in JSON and parenthesized constructs, and with `var` statements that span multiple lines ending in `,`.

The second is super weird. I’ve never seen a case (outside of these sorts of conversations) where you’d want to do write `i\n++\nj`, but, point of fact, that’s parsed as `i; ++j`, not `i++; j`.

The third is well understood, if generally despised. `if (x)\ny()` is equivalent to `if (x) { y() }`. The construct doesn’t end until it reaches either a block, or a statement.

`;` is a valid JavaScript statement, so `if(x);` is equivalent to `if(x){}` or, “If x, do nothing.” This is more commonly applied to loops where the loop check also is the update function. Unusual, but not unheard of.

The fourth is generally the fud-inducing “oh noes, you need semicolons!” case. But, as it turns out, it’s quite easy to *prefix* those lines with semicolons if you don’t mean them to be continuations of the previous line. For example, instead of this:

```js
foo();
[1,2,3].forEach(bar);
```

you could do this:

```js
foo()
;[1,2,3].forEach(bar)
```

The advantage is that the prefixes are easier to notice, once you are accustomed to never seeing lines starting with `(` or `[` without semis.

*End quote from "An Open Letter to JavaScript Leaders Regarding Semicolons".*
> [Relying on automatic semicolon insertion] is quite safe, and perfectly valid JS that every browser understands. Closure compiler, yuicompressor, packer, and jsmin all can properly minify it. There is no performance impact anywhere.
>
> I am sorry that, instead of educating you, the leaders in this language community have given you lies and fear. That was shameful. I recommend learning how statements in JS are actually terminated (and in which cases they are not terminated), so that you can write code that you find beautiful.
>
> In general, `\n` ends a statement unless:
> 1. The statement has an unclosed paren, array literal, or object literal or ends in some
> other way that is not a valid way to end a statement. (For instance, ending with `.`
> or `,`.)
> 2. The line is `--` or `++` (in which case it will decrement/increment the next token.)
> 3. It is a `for()`, `while()`, `do`, `if()`, or `else`, and there is no `{`
> 4. The next line starts with `[`, `(`, `+`, `*`, `/`, `-`, `,`, `.`, or some other
> binary operator that can only be found between two tokens in a single expression.
>
> The first is pretty obvious. Even JSLint is ok with `\n` chars in JSON and parenthesized constructs, and with `var` statements that span multiple lines ending in `,`.
>
> The second is super weird. I’ve never seen a case (outside of these sorts of conversations) where you’d want to do write `i\n++\nj`, but, point of fact, that’s parsed as `i; ++j`, not `i++; j`.
>
> The third is well understood, if generally despised. `if (x)\ny()` is equivalent to `if (x) { y() }`. The construct doesn’t end until it reaches either a block, or a statement.
>
> `;` is a valid JavaScript statement, so `if(x);` is equivalent to `if(x){}` or, “If x, do nothing.” This is more commonly applied to loops where the loop check also is the update function. Unusual, but not unheard of.
>
> The fourth is generally the fud-inducing “oh noes, you need semicolons!” case. But, as it turns out, it’s quite easy to *prefix* those lines with semicolons if you don’t mean them to be continuations of the previous line. For example, instead of this:
>
> ```js
> foo();
> [1,2,3].forEach(bar);
> ```
>
> you could do this:
>
> ```js
> foo()
> ;[1,2,3].forEach(bar)
> ```
>
> The advantage is that the prefixes are easier to notice, once you are accustomed to never seeing lines starting with `(` or `[` without semis.
[1]: http://blog.izs.me/post/2353458699/an-open-letter-to-javascript-leaders-regarding
[2]: http://inimino.org/~inimino/blog/javascript_semicolons
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