From 69e44506c3e9dac74c282be37b55ba7ff122ae74 Mon Sep 17 00:00:00 2001
From: Ilya Kantor <iliakan@gmail.com>
Date: Sun, 31 May 2020 17:18:07 +0300
Subject: [PATCH] minor fixes

---
 .../12-nullish-coalescing-operator/article.md | 43 ++++++++++++-------
 1 file changed, 28 insertions(+), 15 deletions(-)

diff --git a/1-js/02-first-steps/12-nullish-coalescing-operator/article.md b/1-js/02-first-steps/12-nullish-coalescing-operator/article.md
index 7392b81f..ee06d5cb 100644
--- a/1-js/02-first-steps/12-nullish-coalescing-operator/article.md
+++ b/1-js/02-first-steps/12-nullish-coalescing-operator/article.md
@@ -16,22 +16,26 @@ x = (a !== null && a !== undefined) ? a : b;
 
 Here's a longer example.
 
-Let's say, we have a `firstName`, `lastName` or `nickName`, all of them optional.
+Imagine, we have a user, and there are variables `firstName`, `lastName` or `nickName` for their first name, last name and the nick name. All of them may be undefined, if the user decided not to enter any value.
 
-Let's choose the defined one and show it (or "Anonymous" if nothing is set):
+We'd like to display the user name: one of these three variables, or show "Anonymous" if nothing is set.
+
+Let's use the `??` operator to select the first defined one:
 
 ```js run
 let firstName = null;
 let lastName = null;
 let nickName = "Supercoder";
 
-// show the first not-null/undefined variable
+// show the first not-null/undefined value
+*!*
 alert(firstName ?? lastName ?? nickName ?? "Anonymous"); // Supercoder
+*/!*
 ```
 
 ## Comparison with ||
 
-That's very similar to OR `||` operator. Actually, we can replace `??` with `||` in the code above and get the same result.
+The OR `||` operator can be used in the same way as `??`. Actually, we can replace `??` with `||` in the code above and get the same result, as it was described in the [previous chapter](info:logical-operators#or-finds-the-first-truthy-value).
 
 The important difference is that:
 - `||` returns the first *truthy* value.
@@ -39,13 +43,13 @@ The important difference is that:
 
 This matters a lot when we'd like to treat `null/undefined` differently from `0`.
 
-For example:
+For example, consider this:
 
 ```js
 height = height ?? 100;
 ```
 
-This sets `height` to `100` if it's not defined. But if `height` is `0`, then it remains "as is".
+This sets `height` to `100` if it's not defined.
 
 Let's compare it with `||`:
 
@@ -56,17 +60,19 @@ alert(height || 100); // 100
 alert(height ?? 100); // 0
 ```
 
-Here, `height || 100` treats zero height as unset, same as `null`, `undefined` or any other falsy value, depeding on use cases that may be incorrect.
+Here, `height || 100` treats zero height as unset, same as `null`, `undefined` or any other falsy value. So zero becames `100`.
 
-The `height ?? 100` returns `100` only if `height` is exactly `null` or `undefined`.
+The `height ?? 100` returns `100` only if `height` is exactly `null` or `undefined`. So zero remains "as is".
+
+Which behavior is better depends on a particular use case. When zero height is a valid value, that we shouldn't touch, then `??` is preferrable.
 
 ## Precedence
 
 The precedence of the `??` operator is rather low: `7` in the [MDN table](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table).
 
-That's lower than most operators and a bit higher than `=` and `?`.
+So `??` is evaluated after most other operations, but before `=` and `?`.
 
-So if we need to use `??` in a complex expression, then consider adding parentheses:
+If we need to choose a value with `??` in a complex expression, then consider adding parentheses:
 
 ```js run
 let height = null;
@@ -78,14 +84,18 @@ let area = (height ?? 100) * (width ?? 50);
 alert(area); // 5000
 ```
 
-Otherwise, if we omit parentheses, then `*` has the higher precedence and would run first. That would be the same as:
+Otherwise, if we omit parentheses, `*` has the higher precedence than `??` and would run first.
+
+That would work be the same as:
 
 ```js
-// not correct
+// probably not correct
 let area = height ?? (100 * width) ?? 50;
 ```
 
-There's also a related language-level limitation. Due to safety reasons, it's forbidden to use `??` together with `&&` and `||` operators.
+There's also a related language-level limitation.
+
+**Due to safety reasons, it's forbidden to use `??` together with `&&` and `||` operators.**
 
 The code below triggers a syntax error:
 
@@ -93,12 +103,15 @@ The code below triggers a syntax error:
 let x = 1 && 2 ?? 3; // Syntax error
 ```
 
-The limitation is surely debatable, but for some reason it was added to the language specification.
+The limitation is surely debatable, but it was added to the language specification with the purpose to avoid programming mistakes, as people start to switch to `??` from `||`.
 
-Use explicit parentheses to fix it:
+Use explicit parentheses to work around it:
 
 ```js run
+*!*
 let x = (1 && 2) ?? 3; // Works
+*/!*
+
 alert(x); // 2
 ```