Create exercise_04.js

Author: Siyuan Gao

Lesson07/exercise_04.js

@@ -0,0 +1,22 @@
+// 1
+let singers = [];
+// 2
+singers.push({ name: 'miku', age: 16 });
+// 3
+singers[0].name = 'Hatsune Miku'
+console.log(singers);
+// 4
+singers[0].birthday = 'August 31';
+console.log(singers);
+// 5
+console.log(singers[0].name);
+const propertyName = 'name';
+console.log(singers[0][propertyName]);
+// 6
+let myConsole = { name: 'PS4', color: 'black', price: 499, library: []};
+// 7
+console.log(Object.keys(myConsole));
+// 8
+if (myConsole.ramSize) {
+  console.log('ram size is defined.');
+}