new file: javascript/filling-up-array.md

javascript/filling-up-array.md

@@ -0,0 +1,29 @@
+# How to Not Fill Up an `Array`
+
+What gets logged?
+
+```js
+const array = new Array(3).fill([]);
+array[0].push("bytes");
+console.log(array); // [ ["bytes"], ["bytes"], ["bytes"] ]
+```
+
+The key to understanding this one is in knowing that arrays in JavaScript are [reference values](https://ui.dev/primitive-vs-reference-values-in-javascript).
+
+When you call `.fill([])`, what you’re really doing is “filling up” the array with three _references_ to the same array. You can kind of think of it like this.
+
+```js
+const reference = [];
+const array = new Array(3).fill(reference);
+```
+
+Where now, `array` has three elements and they’re all referencing the same `reference` array. Therefore, if you add an item to any of the three elements, since they all point to the same array, it’s _as if_ you’re adding an item to all of them.
+
+To get the same functionality without the referential weirdness, you can use `Array.from`.
+
+```js
+const array = Array.from({ length: 3 }, () => []);
+array[0].push("bytes"); // [ ["bytes"], [], [] ]
+```
+
+[source](https://bytes.dev/archives/231)

javascript/sort-alphabetically.md

@@ -38,3 +38,5 @@ function sortAlphabetically(arr) {
   return arr.sort((a, b) => collator.compare(a.firstName, b.firstName));
 }
 ```
+
+[source](https://bytes.dev/archives/214)