捕捉promise中的错误和拒绝promise[重复]

Question

我编写了一个函数，它返回异步逐行读取文件的promise，但问题是如果文件不存在，就会抛出错误，应用程序崩溃。我已经将代码包围在try-catch块中，但是代码执行从未进入catch块，而是终止。

其次，我可以拒绝promise，然后从promise中返回json对象吗？

像reject（{success:false}）

const fs = require('fs');
const readline = require('readline');

class fileParser{
    readPolicyFile = function(filePath, fileName) {
        return new Promise((resolve, reject) => {
            try {
                let response = {};
                let readInterface = readline.createInterface({
                    input: fs.createReadStream(`${filePath}/${fileName}`),
                    terminal: false
                });
    
                readInterface
                    .on('line', line => {
                        // Do processing here to create the response
                    })
                    .on('close', () => {
                        resolve(response);
                    });
            } catch(err){
                console.log("Inside catach block");
                reject(err);
            }
        })
    }
}


module.exports = new fileParser();




Answer 1

你将永远不会看到在catach块行，因为createReadStream不会抛出一个正常的错误。当它想抛出一个错误时，它会发出错误事件。

您需要的是处理createReadStream的错误（而不是readInterface的）

const fs = require('fs');
const readline = require('readline');

class fileParser {
  readPolicyFile = function (filePath, fileName) {
    return new Promise((resolve, reject) => {
      let response = {};

      // create a stream and handle it's error event
      const stream = fs.createReadStream(`${filePath}/${fileName}`);
      stream.on('error', (error) => {
        reject(error);
        // or reject({success: false}), but why call reject with data
        // If you don't want to handle error of readPolicyFile function, just call resolve({success: false})
      });

      let readInterface = readline.createInterface({
        input: stream,
        terminal: false
      });

      readInterface
        .on('line', line => {
          // Do processing here to create the response
        })
        .on('close', () => {
          resolve(response);
        });
    })
  }
}

module.exports = new fileParser();