异常

输出未定义变量，报错 ReferenceError: a is not defined 。抛出异常后， JavaScript 中断运行。

console.log(1);

console.log(a);

console.log(2);

1

console.log(a);
            ^

ReferenceError: a is not defined

使用 try...catch 处理异常。

console.log(1);

try {
  console.log(2);
  console.log(a);
  console.log(3);
} catch {
  console.log('wrong');
}

console.log(4);

1
2
wrong
4

异常 ​