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/11-var-and-scope/starter.js

@@ -0,0 +1,27 @@
+console.log("var 声明前：", lessonType);
+var lessonType = "JavaScript";
+
+// 如果你取消下面两行注释，会报错，因为 let 在声明前不能访问。
+// console.log("let 声明前：", chapterType);
+// let chapterType = "作用域";
+
+function compareScope() {
+  if (true) {
+    var lessonName = "变量";
+    let chapterName = "作用域";
+    const stage = "进阶";
+
+    console.log("块内：", lessonName, chapterName, stage);
+  }
+
+  // 任务：
+  // 1. 输出 lessonName
+  // 2. 不要直接在这里输出 chapterName，否则会报错
+  // 3. 用一句注释说明为什么
+}
+
+compareScope();
+
+// 任务：
+// 4. 试着重新给 const 声明的值赋值
+// 5. 观察会发生什么