minor fixes

- fix erratas
- fix wrong error message
- add 'run' on runnable example
- add explanation about window.onload property corresponding load event
- add comment about window.onstorage property corresponding storage event

1-js/06-advanced-functions/03-closure/7-let-scope/solution.md

@@ -31,7 +31,7 @@ function func() {
   // hence the error
 */!*
 
-  console.log(x); // ReferenceError: Cannot access 'vx before initialization
+  console.log(x); // ReferenceError: Cannot access 'x' before initialization
 
   let x = 2;
 }

1-js/06-advanced-functions/04-var/article.md

@@ -218,7 +218,7 @@ The Function Expression is wrapped with parenthesis `(function {...})`, because
 
 ```js run
 // Try to declare and immediately call a function
-function() { // <-- Error: Unexpected token (
+function() { // <-- Error: Function statements require a function name
 
   let message = "Hello";