Add hasOne and hasMany

snippets/hasMany.md

@@ -0,0 +1,19 @@
+---
+title: hasMany
+tags: array,beginner
+firstSeen: 2021-07-11T05:00:00-04:00
+---
+
+Checks if an array has more than one value matching the given function.
+
+- Use `Array.prototype.filter()` in combination with `fn` to find all matching array elements.
+- Use `Array.prototype.length` to check if more than one element match `fn`.
+
+```js
+const hasMany = (arr, fn) => arr.filter(fn).length > 1;
+```
+
+```js
+hasMany([1, 3], x => x % 2); // true
+hasMany([1, 2], x => x % 2); // false
+```

snippets/hasOne.md

@@ -0,0 +1,19 @@
+---
+title: hasOne
+tags: array,beginner
+firstSeen: 2021-07-04T05:00:00-04:00
+---
+
+Checks if an array has only one value matching the given function.
+
+- Use `Array.prototype.filter()` in combination with `fn` to find all matching array elements.
+- Use `Array.prototype.length` to check if only one element matches `fn`.
+
+```js
+const hasOne = (arr, fn) => arr.filter(fn).length === 1;
+```
+
+```js
+hasOne([1, 2], x => x % 2); // true
+hasOne([1, 3], x => x % 2); // false
+```