Update differenceBy

snippets/differenceBy.md

@@ -5,7 +5,9 @@ tags: array,intermediate
 
 Returns the difference between two arrays, after applying the provided function to each array element of both.
 
-- Create a `Set` by applying `fn` to each element in `b`, then use `Array.prototype.map()` to apply `fn` to each element in `a`, then `Array.prototype.filter()`
+- Create a `Set` by applying `fn` to each element in `b`.
+- Use `Array.prototype.map()` to apply `fn` to each element in `a`.
+- Use `Array.prototype.filter()` in combination with `fn` on `a` to only keep values not contained in `b`, using `Set.prototype.has()`.
 
 ```js
 const differenceBy = (a, b, fn) => {