Update setting-the-length-of-an-array.md

CHANGELOG.md

@@ -48,6 +48,11 @@ Types of change:
 
 ### Fixed
 
+## January 28th 2021
+
+### Changed
+- [Javascript - Setting The Length of An Array - Update information about empty array items](https://github.com/enkidevs/curriculum/pull/2535)
+
 ## January 27th 2021
 
 ### Added
@@ -137,7 +142,7 @@ Types of change:
 ## January 11th 2021
 
 ### Fixed
-- [Go - Assignment Operators - Fix incorrect RQ answer](https://github.com/enkidevs/curriculum/pull/2536)
+- [Go - Assignment Operators - Fix incorrect RQ answer](https://github.com/enkidevs/curriculum/pull/2536
 
 ## January 5th 2021
 

javascript/javascript-core/javascript-arrays/setting-the-length-of-an-array.md

@@ -5,6 +5,9 @@ category: hack
 tags:
   - introduction
   - obscura
+links:
+  - >-
+    [Array Holes](https://medium.com/better-programming/what-are-holes-in-arrays-3ac5fcbcd1c){website}
 practiceQuestion:
   formats:
     - fill-in-the-gap
@@ -44,11 +47,14 @@ a.length = 4;
 // a = [
 //   "one", 
 //   "two", 
-//   undefined,
-//   undefined
+//   <2 empty items>
 // ]
 ```
 
+Extending an array without adding values would create empty item slots, also called *holes*. An array with *holes* is also referred to as a *sparse* array.
+
+> 💡 Check out the *Learn More* section for more information about *sparse* arrays and *holes*.
+
 Finally, to truncate to zero:
 
 ```javascript
@@ -74,9 +80,9 @@ arr.length = 4;
 ```
 
 - length
-- `[1,2,undefined,undefined]`
+- `[1, 2, <1 empty item>, <1 empty item>]`
 - size
-- `[1,2,undefined,undefined,undefined]`
+- `[1, 2, undefined, undefined]`
 
 
 ---
@@ -95,7 +101,7 @@ names.length = 0;
 // names = ???
 ```
 
-- `["John","Mary","Tom", undefined]`
+- `["John", "Mary", "Tom",  <1 empty item>]`
 - `[ ]`
 - `[undefined,undefined,undefined, undefined]`
 - `["John","Mary","Tom"]`