High Order Functions tutorial

docs/JavaScript_Basics/higher_order_functions.md

@@ -1 +1,26 @@
-# Higher Order Functions
+# Higher Order Functions
+
+Higher-order functions are functions that take other functions as arguments or return functions as their results.
+
+Taking an other function as an argument is often referred as a callback function, because it is called back by the higher-order function. This is a concept that Javascript uses a lot.
+
+For example, the map function on arrays is a higher order function. The map function takes a function as an argument.
+
+```javascript
+const list = [1, 2, 3, 4, 5 ];
+const double = n => n * 2
+
+[1, 2, 3, 4].map(double) // [ 2, 4, 6, 8, 10 ]
+```
+
+
+Or, with an anonymous function:
+```javascript
+const newList = list.map(function (item, index, list) {
+  return item * 2;
+});
+// [ 2, 4, 6, 8, 10 ]
+```
+The map function is one of the many higher-order functions built into the language. sort, reduce, filter, forEach are other examples of higher-order functions built into the language.
+
+Higher-order functions allows you to write simpler and more elegant code.