Aug 16, 2023 · Aug 18, 2023
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
 # Nullish coalescingoperator'??'
 # Nullish coalescingand assignment operators:'??', '??='

 [recent browser="new"]

 ## Nullish coalescing operator (??)

 The nullish coalescing operator is written as two question marks `??`.

 As it treats `null` and `undefined` similarly, we'll use a special term here, in this article. For brevity, we'll say that a value is "defined" when it's neither `null` nor `undefined`.
 */!*
 ```

 ## Comparison with ||
 ### Comparison with ||

 The OR `||` operator can be used in the same way as `??`, as it was described in the [previous chapter](info:logical-operators#or-finds-the-first-truthy-value).


 In practice, the zero height is often a valid value, that shouldn't be replaced with the default. So `??` does just the right thing.

 ## Precedence
 ### Precedence

 The precedence of the `??` operator is the same as `||`. They both equal `3` in the [MDN table](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table).

 alert(x); // 2
 ```

 ## Nullish coalescing assignment (??=)

 Suppose we need to check whether a variable is equal to `null` or `undefined`, and if so, assign some other value to that variable.

 This is how we'd do it now:

 ```js
 let userAge = null;

 if (userAge === null || userAge === undefined) {
  userAge = 18;
 }
 ```

 Looks cumbersome, isn't it? There is an operator more suitable for such tasks. Here's its syntax:

 ```js
 x ??= y
 ```

 The `??=` operator will assign `x` to the value of `y` only if `x` *is not defined (`null`/`undefined`)*.

 Now let's try to rewrite a code fragment we already recognize using the nullish assignment operator `??=`:

 ```js run
 let userAge = null;

 userAge ??= 18;

 alert(userAge) // 18
 ```

 Please note: if `userAge` were not equal to `null`/`undefined`, the expression to the right of `??=` would never be evaluated:

 ```js run
 let userAge = 18;

 userAge ??= alert("wouldn't work");
 userAge ??= 21;
 userAge ??= null;

 alert(userAge) // still 18
 ```

 ## Summary

 - The nullish coalescing operator `??` provides a short way to choose the first "defined" value from a list.

 - The operator `??` has a very low precedence, only a bit higher than `?` and `=`, so consider adding parentheses when using it in an expression.
 - It's forbidden to use it with `||` or `&&` without explicit parentheses.
 - The nullish assignment operator `??=` is used to assign a value to a variable depending on whether it's "defined" or not.
Original file line number	Diff line number	Diff line change
		@@ -1,7 +1,9 @@
		# Nullish coalescingoperator'??'
		# Nullish coalescingand assignment operators:'??', '??='

		[recent browser="new"]

		## Nullish coalescing operator (??)

		The nullish coalescing operator is written as two question marks `??`.

		As it treats `null` and `undefined` similarly, we'll use a special term here, in this article. For brevity, we'll say that a value is "defined" when it's neither `null` nor `undefined`.
Expand DownExpand Up		@@ -59,7 +61,7 @@ alert(firstName ?? lastName ?? nickName ?? "Anonymous"); // Supercoder
		/!
		```

		## Comparison with \|\|
		### Comparison with \|\|

		The OR `\|\|` operator can be used in the same way as `??`, as it was described in the [previous chapter](info:logical-operators#or-finds-the-first-truthy-value).

Expand DownExpand Up		@@ -104,7 +106,7 @@ alert(height ?? 100); // 0

		In practice, the zero height is often a valid value, that shouldn't be replaced with the default. So `??` does just the right thing.

		## Precedence
		### Precedence

		The precedence of the `??` operator is the same as `\|\|`. They both equal `3` in the [MDN table](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table).

Expand DownExpand Up		@@ -154,6 +156,50 @@ let x = (1 && 2) ?? 3; // Works
		alert(x); // 2
		```

		## Nullish coalescing assignment (??=)

		Suppose we need to check whether a variable is equal to `null` or `undefined`, and if so, assign some other value to that variable.

		This is how we'd do it now:

		```js
		let userAge = null;

		if (userAge === null \|\| userAge === undefined) {
		userAge = 18;
		}
		```

		Looks cumbersome, isn't it? There is an operator more suitable for such tasks. Here's its syntax:

		```js
		x ??= y
		```

		The `??=` operator will assign `x` to the value of `y` only if `x` is not defined (`null`/`undefined`).

		Now let's try to rewrite a code fragment we already recognize using the nullish assignment operator `??=`:

		```js run
		let userAge = null;

		userAge ??= 18;

		alert(userAge) // 18
		```

		Please note: if `userAge` were not equal to `null`/`undefined`, the expression to the right of `??=` would never be evaluated:

		```js run
		let userAge = 18;

		userAge ??= alert("wouldn't work");
		userAge ??= 21;
		userAge ??= null;

		alert(userAge) // still 18
		```

		## Summary

		- The nullish coalescing operator `??` provides a short way to choose the first "defined" value from a list.
Expand All		@@ -167,3 +213,4 @@ alert(x); // 2

		- The operator `??` has a very low precedence, only a bit higher than `?` and `=`, so consider adding parentheses when using it in an expression.
		- It's forbidden to use it with `\|\|` or `&&` without explicit parentheses.
		- The nullish assignment operator `??=` is used to assign a value to a variable depending on whether it's "defined" or not.