fix(guide): simplify directory structure

guide/english/javascript/es6/map-function/index.md

@@ -0,0 +1,24 @@
+---
+title: Map Function
+---
+
+## The Map Function
+
+The `map()` function is used for creating a new array from an existing one, applying a function to each one of the elements of the first array.
+
+The original syntax of the map function is:
+```javascript
+  let new_arr = arr.map(function callback(currentValue, index, array) {
+                  // Do some stuff with currentValue (index and array are optionals)
+                })
+```
+
+### Example (ES6):
+
+```javascript
+const myArray_1 = [1, 2, 3, 4];
+const myArray_2 = myArray_1.map(el => el * 2);
+```
+`myArray_2` will contain the elements: `[2, 4, 6, 8]`
+
+`map()` is a method of the `Array` object, so to pass that function to an iterable object it is necessary to make the object an Array.