关于javascript:trycatchfinally使用注意事项

try、catch、finally 用法总结:

1、不论有没有异样，finally 中的代码都会执行

2、当 try、catch 中有 return 时，finally 中的代码仍然会继续执行

3、try 或 catch 外面有 return 语句，finally 外面的表达式依旧会执行，但不影响 try.catch return 的值。

finally 语句执行不会影响 try 或 catch 的 return

  const test = () => {
    let a = 123;
    try {console.log('this is - try - , a =', a);
      return a;
    } catch (error) {console.log('this is - catch - , a =', a);
      return a;
    } finally {console.log('this is - finally -, a =', a);
      a = '000';
      console.log('this is end of - finally -, a =', a);
    }
  };

  console.log(test());

打印后果

// this is - try - , a =  123
// this is - finally -, a =  123
// this is end of - finally -, a =  000
// 123

异样 catch

  const test = () => {
    let a = 123;
    try {console.log('this is - try - , a =', a);
      throw new Error('test error');
      return a;
    } catch (error) {
      a = 9999;
      console.log('this is - catch - , a =', a);
      return a;
    } finally {
      a = '000';
      console.log('this is - finally -, a =', a);
    }
  };
  console.log(test());

打印后果

// this is - try - , a =  123
// this is - catch - , a =  9999
// this is - finally -, a =  000
// 9999

这里要留神返回的不是援用类型。援用类型，finally 的批改会影响函数返回值

4、finally 代码中最好不要蕴含 return，会笼罩 try 和 catch 的 return

  const test = () => {
    let a = 123;
    try {console.log('this is - try - , a =', a);
      throw new Error('test error');
      return a;
    } catch (error) {console.log('this is - catch - , a =', a);
      a = 9999;
      return a;
    } finally {console.log('this is - finally -, a =', a);
      a = '000';
      console.log('this is end of - finally -, a =', a);
      return a;
    }
  };
  console.log(test());

打印后果

// this is - try - , a =  123
// this is - catch - , a =  123
// this is - finally -, a =  9999
// this is end of - finally -, a =  000
// 000