[eslint config] [breaking] add no-useless-escape rule.

Author: ljharb

README.md

@@ -547,6 +547,20 @@ Other Style Guides
   <a name="strings--eval"></a><a name="6.5"></a>
   - [6.5](#strings--eval) Never use `eval()` on a string, it opens too many vulnerabilities.
 
+  <a name="strings--escaping"></a>
+  - [6.6](#strings--escaping) Do not unnecessarily escape characters in strings. eslint: [`no-useless-escape`](http://eslint.org/docs/rules/no-useless-escape)
+
+    > Why? Backslashes harm readability, thus they should only be present when necessary.
+
+    ```javascript
+    // bad
+    const foo = '\'this\' \i\s \"quoted\"';
+
+    // good
+    const foo = '\'this\' is "quoted"';
+    const foo = `'this' is "quoted"`;
+    ```
+
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packages/eslint-config-airbnb/rules/best-practices.js

@@ -113,6 +113,9 @@ module.exports = {
     'no-unused-labels': 2,
     // disallow unnecessary .call() and .apply()
     'no-useless-call': 0,
+    // disallow unnecessary string escaping
+    // http://eslint.org/docs/rules/no-useless-escape
+    'no-useless-escape': 2,
     // disallow use of void operator
     'no-void': 0,
     // disallow usage of configurable warning terms in comments: e.g. todo