Add isPrimitive utility snippet

snippets/isPrimitive.md

@@ -0,0 +1,22 @@
+### isPrimitive
+
+Returns a boolean determining if the supplied value is primitive or not.
+
+Use `Array.includes()` on an array of type strings, supplying the type using `typeof`.
+Since `typeof null` evaluates to `'object'`, it needs to be directly compared.
+
+```js
+const isPrimitive = value =>
+  ['string', 'number', 'symbol', 'boolean', 'undefined'].includes(typeof value) || value === null;
+```
+
+```js
+isPrimitive(window.someNonExistentProperty); // true
+isPrimitive(null); // true
+isPrimitive(50); // true
+isPrimitive('Hello!'); // true
+isPrimitive(false); // true
+isPrimitive(Symbol()); // true
+isPrimitive([]); // false
+isPrimitive(new String('Hello!')); // false
+```