feat: Add JavaScript core exercises and solutions

- Implemented exercises for array high-order methods, memory and execution, switch statements, and final review.
- Added starter and answer files for each exercise to facilitate learning.
- Created a runner HTML file to execute JavaScript code and display console outputs.
- Updated README files to include exercise objectives, tasks, and usage instructions.

03-javascript-core/14-memory-and-execution/answer.js

@@ -0,0 +1,39 @@
+let scoreA = 80;
+let scoreB = scoreA;
+
+scoreB = 95;
+
+console.log("基本类型 scoreA：", scoreA);
+console.log("基本类型 scoreB：", scoreB);
+console.log("基本类型复制后，两个变量互不影响。");
+
+const userA = {
+  name: "小周",
+  city: "上海",
+};
+
+const userB = userA;
+userB.city = "深圳";
+
+console.log("对象 userA：", userA);
+console.log("对象 userB：", userB);
+console.log("对象变量保存的是引用，所以改 userB 会影响 userA。");
+
+function printStepOne() {
+  console.log("步骤一：先进入第一个函数");
+}
+
+function printStepTwo() {
+  console.log("步骤二：再执行第二个函数");
+}
+
+function updateUser(user) {
+  user.city = "杭州";
+  console.log("函数内部修改后的 user：", user);
+}
+
+printStepOne();
+printStepTwo();
+updateUser(userA);
+
+console.log("函数执行结束后的 userA：", userA);