# 异常

console.log(a); // Uncaught ReferenceError: a is not defined.跑异常后面的代码其实不会执行了

var emp = undefined;
console.log(emp.name); // Uncaught TypeError: Cannot read property 'name' of undefined

try {
  console.log(a);
} catch (error) {
  console.error(error); // Uncaught ReferenceError: a is not defined
} finally {
  console.log("总会执行");
}

try {
  var emp = undefined;
  console.log(emp.name);
} catch (error) {
  console.error(error); // TypeError: Cannot read property 'name' of undefined
} finally {
  console.log("总会执行");
}

class ApiError extends Error {
  constructor(url, ...params) {
    super(...params);
    this.name = "ApiError";
    this.url = url;
  }
}

function fetchData() {
  console.log("获取数据...");
  console.log(a);
  throw new ApiError("/api/hello", "404"); //不推荐，应该继承异常对象
}

try {
  fetchData();
} catch (error) {
  if (error instanceof ReferenceError) {
    console.log("程序异常");
  } else if (error instanceof ApiError) {
    console.error(error);
    console.error(error.name); // ApiError
    console.error(error.message); // 404
    console.error(error.url); // /api/hello
  }
}