Rename js snippets

snippets/js/s/function-based-array-element-uniqueness.md

@@ -0,0 +1,23 @@
+---
+title: Check if all array elements are unique based on function
+type: snippet
+language: javascript
+tags: [array]
+cover: digital-nomad-10
+dateModified: 2021-01-08T00:23:44+02:00
+---
+
+Checks if all elements in an array are unique, based on the provided mapping function.
+
+- Use `Array.prototype.map()` to apply `fn` to all elements in `arr`.
+- Create a new `Set` from the mapped values to keep only unique occurrences.
+- Use `Array.prototype.length` and `Set.prototype.size` to compare the length of the unique mapped values to the original array.
+
+```js
+const allUniqueBy = (arr, fn) => arr.length === new Set(arr.map(fn)).size;
+```
+
+```js
+allUniqueBy([1.2, 2.4, 2.9], Math.round); // true
+allUniqueBy([1.2, 2.3, 2.4], Math.round); // false
+```