Add simple closure example

advance_js/closures.js

@@ -0,0 +1,66 @@
+// Closure
+// A function with access to its own private variables
+
+// problem with global variables
+// var count = 0;
+
+// function countBirds() {
+//   count += 1;
+//   return count + ' bird';
+// }
+
+// function countDogs() {
+//   count += 1;
+//   return count + ' dogs';
+// }
+
+// function makeBirdCounter() {
+//   var count = 0;
+//   return function() {
+//     count += 1;
+//     return count + ' birds';
+//   }
+// }
+
+// function makeDogCounter() {
+//   var count = 0;
+//   return function() {
+//     count += 1;
+//     return count + ' dogs';
+//   }
+// }
+
+// Refactor
+function makeCounter(noun) {
+  var count = 0;
+  return function() {
+    count += 1;
+    return count + ' ' + noun;
+  }
+}
+
+var birds = 3;
+
+// outer function
+function dogHouse() {
+  var dogs = 8;
+
+  // 1.0
+  // console.log(birds); // 3
+  // console.log(dogs); // 8
+  // This won't be avaliable outside the function
+
+  // inner function
+  function showDogs() {
+    // inner function has access to outer function 
+    console.log(dogs);
+  }
+  return showDogs;
+}
+
+// 1.0
+// console.log(birds); // 3
+// console.log(dogs); // undefined
+
+var getDogs = dogHouse();
+getDogs(); //8