update snippets 16-31

snippets/difference.md

@@ -6,5 +6,8 @@ Create a `Set` from `b`, then use `Array.filter()` on `a` to only keep values no
 
 ```js
 const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); };
-// difference([1,2,3], [1,2,4]) -> [3]
+```
+
+```js
+difference([1,2,3], [1,2,4]) -> [3]
 ```