const learningStatus = "review";
const records = ["变量", "条件", "函数", null, "对象"];

let optionalNote;
const finalComment = null;
let statusText = "";
const finishedRecords = [];

switch (learningStatus) {
  case "basic":
    statusText = "正在完成基础阶段";
    break;
  case "review":
    statusText = "正在进入总复习";
    break;
  case "done":
    statusText = "当前阶段已经完成";
    break;
  default:
    statusText = "状态未知";
    break;
}

console.log("状态说明：", statusText);
console.log("optionalNote：", optionalNote);
console.log("optionalNote 是否为 undefined：", optionalNote === undefined);
console.log("finalComment：", finalComment);
console.log("finalComment 是否为 null：", finalComment === null);

for (let index = 0; index < records.length; index += 1) {
  const currentRecord = records[index];

  if (currentRecord === undefined || currentRecord === null) {
    console.log(`第 ${index + 1} 项为空值，停止读取。`);
    break;
  }

  finishedRecords.push(currentRecord);
}

console.log("停止前已读取内容：", finishedRecords);