Question

我正在Node中构建一个服务器，它将搜索文件夹以查看XML文件是否存在（glob），如果存在，则将（fs）中的文件作为JSON对象（xml2js）读取并最终存储它在某个地方的数据库中。我想要将解析器的结果输出到另一个变量中，以便我可以对数据执行其他操作。据我所知，有些东西是同步运行的，但是我无法弄清楚如何阻止它，让我等到它完成继续前进。

我将我的功能分离到app.js的其他地方的控制器：

app.controller.js

const fs = require('fs-extra');
const glob = require('glob');
const xml2js = require('xml2js');

exports.requests = {};

exports.checkFileDrop = async () => {
  console.log('Checking for xml in filedrop...');
  // this is the only place await works...
  await glob('./filedrop/ALLREQUESTS-*.xml', (err, files) => {
    var parser = new xml2js.Parser();
    // this is looking for a specific file now, which I'll address later once I can figure out this issue
    fs.readFile('./filedrop/ALLREQUESTS-20170707.xml', 'utf16le', function (err, data) { 
      if (err) {
        console.log('ERROR: ', err);
      } else {
        parser.parseString(data, (err, result) => {
          if (err) {
            console.log('ERROR: ', err);
          } else {
            console.log('data found');
            exports.requests = JSON.stringify(result.Records.Record);
            // data is outputted here correctly
            console.log(exports.requests);
            // this doesn't even seem to want to save to exports.requests anyways...
          }
        });
      }
    });
  });
}

app.js

const appController = require('./controllers/app.controller');

// check if there is file in filedrop
appController.checkFileDrop();
// prints out an empty object
console.log(appController.requests);
// can't do anything if it doesn't exist yet
appController.saveToDB(appController.requests);

Answer 1

await将等待Promise值解析，否则它将仅包装在promise中给出的值并立即解决promise。在您的示例中，

await glob('./filedrop/ALLREQUESTS-*.xml', (err, files) => {

对glob的调用不会返回Promise，因此await基本上没用。所以你需要自己创造承诺。

exports.checkFileDrop = async () => {
  console.log('Checking for xml in filedrop...');

  const files = await new Promise((resolve, reject) => glob('./filedrop/ALLREQUESTS-*.xml', (err, files) => {
    if (err) reject(err);
    else resolve(files);
  });

  const parser = new xml2js.Parser();

  const data = await new Promise((resolve, reject) => fs.readFile('./filedrop/ALLREQUESTS-20170707.xml', 'utf16le', function (err, data) {
    if (err) reject(err);
    else resolve(data);
  });

  const result = await new Promise((resolve, reject) => parser.parseString(data, (err, result) => {
    if (err) reject(err);
    else resolve(result);
  });

  console.log('data found');

  const requests = JSON.stringify(result.Records.Record);

  console.log(requests);
}

注意，现在这个函数将拒绝它返回的promise，而不是强制记录错误。

你也可以用帮助器压缩它。例如，节点8包括util.promisify以使这样的代码更容易编写，例如

const util = require('util');

exports.checkFileDrop = async () => {
  console.log('Checking for xml in filedrop...');

  const files = await util.promisify(glob)('./filedrop/ALLREQUESTS-*.xml');
  const parser = new xml2js.Parser();

  const data = await util.promisify(fs.readFile)('./filedrop/ALLREQUESTS-20170707.xml', 'utf16le');

  const result = await util.promisify(parser.parseString.bind(parser))(data);

  console.log('data found');

  const requests = JSON.stringify(result.Records.Record);

  console.log(requests);
}

Answer 2

您可以使用async / await

import fs from 'fs';
import { promisify } from 'util';

const xmlToJson = async filePath => {
  const parser = new xml2js.Parser
  try {
    const data = await fs.promises.readFile(filePath, 'utf8')
    const result = await promisify(parser.parseString)(data);
    const requests = JSON.stringify(result.merchandiser.product);
    return requests
  }
  catch(err) {
    console.log(err)
  }
}

如何从ES6中的解析器中获取xml2js结果？

2 个答案: