Added a dot notation example

Author: luc4leone

1-js/04-object-basics/01-object/article.md

@@ -105,7 +105,6 @@ That's because the dot requires the key to be a valid variable identifier. That
 
 There's an alternative "square bracket notation" that works with any string:
 
-
 ```js run
 let user = {};
 
@@ -130,7 +129,7 @@ let key = "likes birds";
 user[key] = true;
 ```
 
-Here, the variable `key` may be calculated at run-time or depend on the user input. And then we use it to access the property. That gives us a great deal of flexibility. The dot notation cannot be used in a similar way.
+Here, the variable `key` may be calculated at run-time or depend on the user input. And then we use it to access the property. That gives us a great deal of flexibility. 
 
 For instance:
 
@@ -146,6 +145,17 @@ let key = prompt("What do you want to know about the user?", "name");
 alert( user[key] ); // John (if enter "name")
 ```
 
+The dot notation cannot be used in a similar way.
+
+```js run
+let user = {
+  name: "John",
+  age: 30
+};
+
+let key = "name";
+user.key // undefined
+```
 
 ### Computed properties