Finished Module 1: Writing modular code with functions

1_writing_modular_code_with_functions.md

@@ -118,7 +118,7 @@ where:
 
 ## How Closure Work
 
-Local variable within function has short life span, as it's out of scope as function finish execution. But sometime we want to hold the variable (e.g. `counter` within function)
+Local variable within function has short life span, as it's out of scope as function finish execution. But sometime we want to hold the variable (e.g. `counter` within function), we can use closure.
 
 e.g. w/o closure
 
@@ -139,8 +139,25 @@ let greeting = (function() {
     let getMessage = function(){
         return message;
     };
+    // Use closure
     return {
         getMessage: getMessage,
     }
-})
+})();
+console.log(greeting.getMessage()); // Hello
+```
+
+e.g. closure used for counter
+
+```javascript
+function setupCounter(val){
+    return function counter() {
+        return val++;
+    }
+}
+let counter1 = setupCounter(0);
+console.log(counter1()); // 0
+console.log(counter1()); // 1
+let counter2 = setupCounter(10);
+console.log(counter2()); // 10
 ```