diff --git a/README.md b/README.md
index cad3dbcba..3480f7f8e 100644
--- a/README.md
+++ b/README.md
@@ -16,6 +16,7 @@
 * [Count occurrences of a value in array](#count-occurrences-of-a-value-in-array)
 * [Current URL](#current-url)
 * [Curry](#curry)
+* [Deep flatten array](#deep-flatten-array)
 * [Difference between arrays](#difference-between-arrays)
 * [Distance between two points](#distance-between-two-points)
 * [Divisible by number](#divisible-by-number)
@@ -115,7 +116,7 @@ const palindrome = str =>
 Use `reduce()` to increment a counter each time you encounter the specific value inside the array.
 
 ```js
-const countOccurrences = (arr, value) => arr.reduce((a, v) => v===value ? a + 1 : a + 0, 0);
+const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
 // countOccurrences([1,1,2,1,2,3], 1) -> 3
 ```
 
@@ -141,6 +142,17 @@ const curry = f =>
 // curry(Math.pow)(2)(10) -> 1024
 ```
 
+### Deep flatten array
+
+Use recursion.
+Use `reduce()` to get all elements that are not arrays, flatten each element that is an array.
+
+```js
+const deepFlatten = arr =>
+  arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
+// deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]
+```
+
 ### Difference between arrays
 
 Use `filter()` to remove values that are part of `values`, determined using `includes()`.
@@ -173,8 +185,7 @@ const isDivisible = (dividend, divisor) => dividend % divisor === 0;
 Use `replace()` to escape special characters.
 
 ```js
-const escapeRegExp = s =>
-  s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
 // escapeRegExp('(test)') -> \\(test\\)
 ```
 
@@ -225,13 +236,11 @@ const unique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
 
 ### Flatten array
 
-Use recursion.
-Use `reduce()` to get all elements that are not arrays, flatten each element that is an array.
+Use `reduce()` to get all elements inside the array and `concat()` to flatten them.
 
 ```js
-const flatten = arr =>
-  arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
-// flatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]
+const flatten = arr => arr.reduce( (a, v) => a.concat(v), []);
+// flatten([1,[2],3,4) -> [1,2,3,4]
 ```
 
 ## Get scroll position
diff --git a/snippets/count-occurrences-of-a-value-in-array.md b/snippets/count-occurrences-of-a-value-in-array.md
index 552ad9f39..89e3b5b6d 100644
--- a/snippets/count-occurrences-of-a-value-in-array.md
+++ b/snippets/count-occurrences-of-a-value-in-array.md
@@ -3,6 +3,6 @@
 Use `reduce()` to increment a counter each time you encounter the specific value inside the array.
 
 ```js
-const countOccurrences = (arr, value) => arr.reduce((a, v) => v===value ? a + 1 : a + 0, 0);
+const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
 // countOccurrences([1,1,2,1,2,3], 1) -> 3
 ```
diff --git a/snippets/deep-flatten-array.md b/snippets/deep-flatten-array.md
new file mode 100644
index 000000000..545c4c8d4
--- /dev/null
+++ b/snippets/deep-flatten-array.md
@@ -0,0 +1,10 @@
+### Deep flatten array
+
+Use recursion.
+Use `reduce()` to get all elements that are not arrays, flatten each element that is an array.
+
+```js
+const deepFlatten = arr =>
+  arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
+// deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]
+```
diff --git a/snippets/escape-regular-expression.md b/snippets/escape-regular-expression.md
index 4bd77a0d9..fb204a451 100644
--- a/snippets/escape-regular-expression.md
+++ b/snippets/escape-regular-expression.md
@@ -3,7 +3,6 @@
 Use `replace()` to escape special characters.
 
 ```js
-const escapeRegExp = s =>
-  s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
 // escapeRegExp('(test)') -> \\(test\\)
 ```
diff --git a/snippets/flatten-array.md b/snippets/flatten-array.md
index f3b1c9f4b..c4afd4847 100644
--- a/snippets/flatten-array.md
+++ b/snippets/flatten-array.md
@@ -1,10 +1,8 @@
 ### Flatten array
 
-Use recursion.
-Use `reduce()` to get all elements that are not arrays, flatten each element that is an array.
+Use `reduce()` to get all elements inside the array and `concat()` to flatten them.
 
 ```js
-const flatten = arr =>
-  arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
-// flatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]
+const flatten = arr => arr.reduce( (a, v) => a.concat(v), []);
+// flatten([1,[2],3,4) -> [1,2,3,4]
 ```