change var to let (#23172)

change var to let

guide/english/javascript/loops/for-in-loop/index.md

@@ -18,14 +18,15 @@ for (variable in object) {
 ## Examples
 ```js
 // Initialize object.
-var a = { "a": "Athens", "b": "Belgrade", "c": "Cairo" };
+const a = { "a": "Athens", "b": "Belgrade", "c": "Cairo" };
 
 // Iterate over the properties.
-var s = "";
+let s = "";
-for (var key in a) {
+for (let key in a) {
   s += key + ": " + a[key];
   s += "<br />";
 }
+
 document.write (s);
 
 // Output:
@@ -34,15 +35,15 @@ document.write (s);
 // c: Cairo
 
 // Initialize the array.
-var arr = new Array("zero", "one", "two");
+let arr = new Array("zero", "one", "two");
 
 // Add a few expando properties to the array.
 arr["orange"] = "fruit";
 arr["carrot"] = "vegetable";
 
 // Iterate over the properties and elements.
-var s = "";
+let s = "";
-for (var key in arr) {
+for (let key in arr) {
     s += key + ": " + arr[key];
     s += "<br />";
 }