Merge pull request #579 from tomekwi/fix-braces-text

[guide] Bring back note about braces

Author: ljharb

README.md

@@ -699,7 +699,7 @@ Other Style Guides
     });
     ```
 
-  - [8.2](#8.2) <a name='8.2'></a> If the function body consists of a single expression, feel free to omit the braces and use the implicit return. Otherwise use a `return` statement.
+  - [8.2](#8.2) <a name='8.2'></a> If the function body consists of a single expression, omit the braces and use the implicit return. Otherwise, keep the braces and use a `return` statement.
 
     > Why? Syntactic sugar. It reads well when multiple functions are chained together.
 
@@ -743,18 +743,36 @@ Other Style Guides
     ```
 
 
-  - [8.4](#8.4) <a name='8.4'></a> If your function only takes a single argument, feel free to omit the parentheses.
+  - [8.4](#8.4) <a name='8.4'></a> If your function takes a single argument and doesn’t use braces, omit the parentheses. Otherwise, always include parentheses around arguments.
 
     > Why? Less visual clutter.
 
     eslint rules: [`arrow-parens`](http://eslint.org/docs/rules/arrow-parens.html).
 
     ```js
+    // bad
+    [1, 2, 3].map((x) => x * x);
+
     // good
     [1, 2, 3].map(x => x * x);
 
     // good
-    [1, 2, 3].reduce((y, x) => x + y);
+    [1, 2, 3].map(number => (
+      `A long string with the ${number}. It’s so long that we’ve broken it ` +
+      'over multiple lines!'
+    ));
+
+    // bad
+    [1, 2, 3].map(x => {
+      const y = x + 1;
+      return x * y;
+    });
+
+    // good
+    [1, 2, 3].map((x) => {
+      const y = x + 1;
+      return x * y;
+    });
     ```
 
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