javascript-101/arrays: add info on second parameter of .slice()

Author: arthurvr

page/javascript-101/arrays.md

@@ -160,7 +160,7 @@ myArray.shift();   // [ 2 , 7 ]
 
 ### .slice()
 
-Extracts a part of the array and returns that part in a new array. This method takes one parameter, which is the starting index:
+Extracts a part of the array and returns that part in a new array. This method takes one required parameter, which is the starting index:
 
 ```
 // Slicing
@@ -172,6 +172,12 @@ console.log( myArray );  // [ 1, 2, 3, 4, 5, 6, 7, 8 ]
 console.log( newArray ); // [ 4, 5, 6, 7, 8 ]
 ```
 
+The `.slice()` method takes an optional second parameter, the end index.
+
+```
+console.log( [ 1, 2, 3, 4, 5, 6, 7, 8 ].slice( 2, 5 ) ); // [ 3, 4, 5 ]
+```
+
 ### .splice()
 
 Removes a certain amount of elements and adds new ones at the given index. It takes at least three parameters: