Merge pull request #322 from cyh0968/issue23

Complete issue23: add more exercise on map

JavaScript_Advance/map_object.js

@@ -59,4 +59,48 @@ for (const amount of recipeMap.values()) {
 // iterate over [key, value] entries
 for (const entry of recipeMap) { // the same as of recipeMap.entries()
   alert(entry); // cucumber,500 (and so on)
-}
+}
+
+/*
+Loop with forEach
+Instead of using for loop, forEach can be used.
+
+map.forEach(function(value, key){
+
+});
+
+or with array function
+
+map.forEach((value, key) => {
+
+})
+
+*/
+
+recipeMap.forEach((value, key) => {
+  alter(key + " = " + value);
+});
+
+/*
+Convert To Arrays
+A map obejct can be convert to arrays
+
+var array = Array.from(map) - create an array of the key-value pairs
+
+var array = Array.from(map.value()) - Create an array of the values
+
+var array = Array.from(map.key()) - Create an array of the keys
+
+*/
+
+// create an array of the key-value pairs
+const keyValArr = Array.from(recipeMap);
+alter(keyValArr);
+
+// Create an array of the values
+const ValArr = Array.from(recipeMap);
+alter(ValArr);
+
+// Create an array of the keys
+const keyArr = Array.from(recipeMap);
+alter(keyArr);

docs/JavaScript_Advance/map_object.md

@@ -64,3 +64,54 @@ iterate over [key, value] entries
       alert(entry); // cucumber,500 (and so on)
     }
 ```
+
+Loop with forEach
+Instead of using for loop, forEach can be used.
+
+```js
+map.forEach(function(value, key){
+
+});
+```
+or with array function
+```js
+map.forEach((value, key) => {
+
+})
+```
+
+```js
+recipeMap.forEach((value, key) => {
+  alter(key + " = " + value);
+});
+```
+Convert To Arrays
+A map obejct can be convert to arrays
+
+```js
+var array = Array.from(map) // create an array of the key-value pairs
+
+var array = Array.from(map.value()) // Create an array of the values
+
+var array = Array.from(map.key()) // Create an array of the keys
+
+```
+
+Create an array of the key-value pairs
+```js
+const keyValArr = Array.from(recipeMap);
+alter(keyValArr);
+```
+
+Create an array of the values
+```js
+const ValArr = Array.from(recipeMap);
+alter(ValArr);
+```
+
+Create an array of the keys
+```js
+const keyArr = Array.from(recipeMap);
+alter(keyArr);
+```
+