From 6abc7b72dfb824a372379708ca39340b2c7abc03 Mon Sep 17 00:00:00 2001
From: Milos Djermanovic <milos.djermanovic@gmail.com>
Date: Mon, 26 Aug 2019 19:24:55 +0200
Subject: [PATCH] Docs: Document the exception in no-unsafe-negation (#12161)

---
 docs/rules/no-unsafe-negation.md | 32 +++++++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/docs/rules/no-unsafe-negation.md b/docs/rules/no-unsafe-negation.md
index 8e1428ea959..880e9f64481 100644
--- a/docs/rules/no-unsafe-negation.md
+++ b/docs/rules/no-unsafe-negation.md
@@ -39,10 +39,36 @@ if (!(key in object)) {
 if (!(obj instanceof Ctor)) {
     // obj is not an instance of Ctor
 }
+```
+
+### Exception
+
+For rare situations when negating the left operand is intended, this rule allows an exception.
+If the whole negation is explicitly wrapped in parentheses, the rule will not report a problem.
+
+Examples of **correct** code for this rule:
+
+```js
+/*eslint no-unsafe-negation: "error"*/
+
+if ((!foo) in object) {
+    // allowed, because the negation is explicitly wrapped in parentheses
+    // it is equivalent to (foo ? "false" : "true") in object
+    // this is allowed as an exception for rare situations when that is the intended meaning
+}
+
+if(("" + !foo) in object) {
+    // you can also make the intention more explicit, with type conversion
+}
+```
+
+Examples of **incorrect** code for this rule:
+
+```js
+/*eslint no-unsafe-negation: "error"*/
 
-if(("" + !key) in object) {
-    // make operator precedence and type conversion explicit
-    // in a rare situation when that is the intended meaning
+if (!(foo) in object) {
+    // this is not an allowed exception
 }
 ```