Merge pull request #472 from tomekwi/implicit-return-#438

Implicit return + single expression

README.md

@@ -593,16 +593,18 @@
     ```javascript
     // bad
     [1, 2, 3].map(function (x) {
-      return x * x;
+      const y = x + 1;
+      return x * y;
     });
 
     // good
     [1, 2, 3].map((x) => {
-      return x * x;
+      const y = x + 1;
+      return x * y;
     });
     ```
 
-  - [8.2](#8.2) <a name='8.2'></a> If the function body fits on one line and there is only a single argument, feel free to omit the braces and parentheses, and use the implicit return. Otherwise, add the parentheses, braces, and use a `return` statement.
+  - [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.
 
   > Why? Syntactic sugar. It reads well when multiple functions are chained together.
 
@@ -610,12 +612,50 @@
 
     ```javascript
     // good
+    [1, 2, 3].map(number => `A string containing the ${number}.`);
+
+    // bad
+    [1, 2, 3].map(number => {
+      const nextNumber = number + 1;
+      `A string containing the ${nextNumber}.`;
+    });
+
+    // good
+    [1, 2, 3].map(number => {
+      const nextNumber = number + 1;
+      return `A string containing the ${nextNumber}.`;
+    });
+    ```
+
+  - [8.3](#8.3) <a name='8.3'></a> In case the expression spans over multiple lines, wrap it in parentheses for better readability.
+
+  > Why? It shows clearly where the function starts and ends.
+
+    ```js
+    // bad
+    [1, 2, 3].map(number => 'As time went by, the string containing the ' +
+      `${number} became much longer. So we needed to break it over multiple ` +
+      'lines.'
+    );
+
+    // good
+    [1, 2, 3].map(number => (
+      `As time went by, the string containing the ${number} became much ` +
+      'longer. So we needed to break it over multiple lines.'
+    ));
+    ```
+
+
+  - [8.4](#8.4) <a name='8.4'></a> If your function only takes a single argument, feel free to omit the parentheses.
+
+  > Why? Less visual clutter.
+
+    ```js
+    // good
     [1, 2, 3].map(x => x * x);
 
     // good
-    [1, 2, 3].reduce((total, n) => {
-      return total + n;
-    }, 0);
+    [1, 2, 3].reduce((y, x) => x + y);
     ```
 
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