[guide] Spread for convert array-like objects, Array.from for mapping airbnb#1084

Author: bl00mber

.travis.yml

@@ -9,11 +9,11 @@ before_install:
   - 'if [ "${TRAVIS_NODE_VERSION}" = "0.6" ]; then npm install -g [email protected] ; elif [ "${TRAVIS_NODE_VERSION}" != "0.9" ]; then case "$(npm --version)" in 1.*) npm install -g [email protected] ;; 2.*) npm install -g npm@2 ;; esac ; fi'
   - 'if [ "${TRAVIS_NODE_VERSION%${TRAVIS_NODE_VERSION#[0-9]}}" = "0" ] || [ "${TRAVIS_NODE_VERSION:0:4}" = "iojs" ]; then npm install -g [email protected] ; elif [ "${TRAVIS_NODE_VERSION}" != "0.6" ] && [ "${TRAVIS_NODE_VERSION}" != "0.9" ]; then npm install -g npm; fi'
 install:
-  - 'cd "packages/${PACKAGE}"'
+  - 'if [ -n "${PACKAGE-}" ]; then cd "packages/${PACKAGE}"; fi'
   - 'if [ "${TRAVIS_NODE_VERSION}" = "0.6" ]; then nvm install 0.8 && npm install -g [email protected] && npm install -g [email protected] && npm install -g npm@2 && npm install && nvm use "${TRAVIS_NODE_VERSION}"; else npm install; fi;'
   - 'if [ -n "${ESLINT}" ]; then npm install --no-save "eslint@${ESLINT}"; fi'
 script:
-  - 'if [ -n "${PREPUBLISH-}" ]; then npm run pretravis && npm run prepublish && npm run posttravis; else npm run travis; fi'
+  - 'if [ -n "${PREPUBLISH-}" ]; then npm run pretravis && npm run prepublish && npm run posttravis; elif [ -n "${LINT-}" ]; then npm run lint; else npm run travis; fi'
 sudo: false
 env:
   matrix:
@@ -26,6 +26,8 @@ matrix:
       env: PREPUBLISH=true ESLINT=4 PACKAGE=eslint-config-airbnb
     - node_js: "node"
       env: PREPUBLISH=true ESLINT=4 PACKAGE=eslint-config-airbnb-base
+    - node_js: "node"
+      env: LINT=true
   allow_failures:
     - node_js: "7"
     - node_js: "5"

README.md

@@ -364,15 +364,31 @@ Other Style Guides
     ```
 
   <a name="arrays--from"></a><a name="4.4"></a>
-  - [4.4](#arrays--from) To convert an array-like object to an array, use [Array.from](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/from).
+  - [4.4](#arrays--from) To convert an array-like object to an array, use spreads `...` instead of [Array.from](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/from).
 
     ```javascript
     const foo = document.querySelectorAll('.foo');
+
+    // good
     const nodes = Array.from(foo);
+
+    // best
+    const nodes = [...foo];
+    ```
+
+  <a name="arrays--mapping"></a>
+  - [4.5](#arrays--mapping) Use [Array.from](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/from) instead of spread `...` for mapping over iterables, because it avoids creating an intermediate array.
+
+    ```javascript
+    // bad
+    const bar = [...foo].map(mapper);
+
+    // good
+    const bar = Array.from(foo, mapper);
     ```
 
   <a name="arrays--callback-return"></a><a name="4.5"></a>
-  - [4.5](#arrays--callback-return) Use return statements in array method callbacks. It’s ok to omit the return if the function body consists of a single statement returning an expression without side effects, following [8.2](#arrows--implicit-return). eslint: [`array-callback-return`](http://eslint.org/docs/rules/array-callback-return)
+  - [4.6](#arrays--callback-return) Use return statements in array method callbacks. It’s ok to omit the return if the function body consists of a single statement returning an expression without side effects, following [8.2](#arrows--implicit-return). eslint: [`array-callback-return`](http://eslint.org/docs/rules/array-callback-return)
 
     ```javascript
     // good
@@ -420,8 +436,8 @@ Other Style Guides
     });
     ```
 
-<a name="arrays--bracket-newline"></a>
-  - [4.6](#arrays--bracket-newline) Use line breaks after open and before close array brackets if an array has multiple lines
+  <a name="arrays--bracket-newline"></a>
+  - [4.7](#arrays--bracket-newline) Use line breaks after open and before close array brackets if an array has multiple lines
 
   ```javascript
   // bad
@@ -2511,7 +2527,7 @@ Other Style Guides
 
 ## Commas
 
-<a name="commas--leading-trailing"></a><a name="19.1"></a>
+  <a name="commas--leading-trailing"></a><a name="19.1"></a>
   - [20.1](#commas--leading-trailing) Leading commas: **Nope.** eslint: [`comma-style`](http://eslint.org/docs/rules/comma-style.html) jscs: [`requireCommaBeforeLineBreak`](http://jscs.info/rule/requireCommaBeforeLineBreak)
 
     ```javascript
@@ -3169,7 +3185,7 @@ Other Style Guides
     eslint: [`no-restricted-globals`](http://eslint.org/docs/rules/no-restricted-globals)
 
     > Why? The global `isNaN` coerces non-numbers to numbers, returning true for anything that coerces to NaN.
-    If this behavior is desired, make it explicit.
+    > If this behavior is desired, make it explicit.
 
     ```javascript
     // bad
@@ -3186,7 +3202,7 @@ Other Style Guides
     eslint: [`no-restricted-globals`](http://eslint.org/docs/rules/no-restricted-globals)
 
     > Why? The global `isFinite` coerces non-numbers to numbers, returning true for anything that coerces to a finite number.
-    If this behavior is desired, make it explicit.
+    > If this behavior is desired, make it explicit.
 
     ```javascript
     // bad

packages/eslint-config-airbnb-base/CHANGELOG.md

@@ -1,7 +1,7 @@
 12.0.0 / 2017-09-02
 ==================
  - [deps] [breaking] require `eslint` v4
-   - enable `function-paren-newline`, `for-direction`, `getter-return`, `no-compare-neg-zero`, `semi-style`, `object-curly-newline`, `no-buffer-constructor`, `no-restricted-globals`, `switch-colon-spacing`, `template-tag-spacing`, `prefer-promise-reject-errors`, `prefer-restructuring`
+   - enable `function-paren-newline`, `for-direction`, `getter-return`, `no-compare-neg-zero`, `semi-style`, `object-curly-newline`, `no-buffer-constructor`, `no-restricted-globals`, `switch-colon-spacing`, `template-tag-spacing`, `prefer-promise-reject-errors`, `prefer-destructuring`
    - improve `indent`, `no-multi-spaces`, `no-trailing-spaces`, `no-underscore-dangle`
  - [breaking] move `comma-dangle` to Stylistic Issues (#1514)
  - [breaking] Rules prohibiting global isNaN, isFinite (#1477)