javascript - Nodejs 从嵌套函数返回结果

Question

这个问题已经有答案了:

How do I return the response from an asynchronous call? (42 个回答)

已关闭 3 年前。

我很难理解如何在 JS 中操作堆栈希望这个练习能帮助我..

所以我尝试编写一个函数来进行soap xml 调用并解析数据。然后在调用时返回解析后的数据。

当我调用该函数时，我可以将其结果发送到 console.log，但我无法让它返回结果，因此我可以将其存储在变量等中。它返回未定义。

代码如下:

var request = require('request');
var DOMParser = require('xmldom').DOMParser;

function query (entity,field,op,expression,elementToParse){
   xml = 
        `<?xml version="1.0" encoding="utf-8"?>
           <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" 
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
           xmlns:xsd="http://www.w3.org/2001/XMLSchema">
           <soap:Header>
           <AutotaskIntegrations xmlns="http://autotask.net/ATWS/v1_6/">
           <IntegrationCode>H2FATPVKPDN25IXIBSMN5K66XAA</IntegrationCode>
           </AutotaskIntegrations>
           </soap:Header>
           <soap:Body>
           <query xmlns="http://autotask.net/ATWS/v1_6/">
           <sXML><![CDATA[<queryxml><entity>${entity}</entity><query><field>${field}<expression 
           op="${op}">${expression}</expression></field></query></queryxml>]]></sXML>
           </query>
           </soap:Body>
           </soap:Envelope>`;


   options = {
      'method': 'POST',
      'url': 'https://webservices15.autotask.net/ATServices/1.6/atws.asmx',
      'headers': {
         'Content-Type': 'text/xml',
         'Authorization':'Auth Goes Here'
      },

      body: xml

      };

    request(options, function (error, response) { 
      if (error) throw new Error(error);
       text =  response.body;
       parser =  new DOMParser();
       xmlDoc =  parser.parseFromString(text,"text/xml");
       xmlResult = xmlDoc.getElementsByTagName(`${elementToParse}`)[0].childNodes[0].nodeValue;
       **console.log(xmlResult)**
      });
}

query('Ticket','TicketNumber','BeginsWith','T2019','id') 
// returns result if i log the data in REQUEST
//returns undefined otherwise

Answer 1

您应该使用Promises对 future 事件使用react并处理 JavaScript 中的异步代码执行:

var request = require('request');
var DOMParser = require('xmldom').DOMParser;

function query(entity, field, op, expression, elementToParse) {
    xml =
        `<?xml version="1.0" encoding="utf-8"?>
           <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" 
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
           xmlns:xsd="http://www.w3.org/2001/XMLSchema">
           <soap:Header>
           <AutotaskIntegrations xmlns="http://autotask.net/ATWS/v1_6/">
           <IntegrationCode>H2FATPVKPDN25IXIBSMN5K66XAA</IntegrationCode>
           </AutotaskIntegrations>
           </soap:Header>
           <soap:Body>
           <query xmlns="http://autotask.net/ATWS/v1_6/">
           <sXML><![CDATA[<queryxml><entity>${entity}</entity><query><field>${field}<expression 
           op="${op}">${expression}</expression></field></query></queryxml>]]></sXML>
           </query>
           </soap:Body>
           </soap:Envelope>`;


    options = {
        'method': 'POST',
        'url': 'https://webservices15.autotask.net/ATServices/1.6/atws.asmx',
        'headers': {
            'Content-Type': 'text/xml',
            'Authorization': 'Auth Goes Here'
        },

        body: xml

    };
    return new Promise((resolve, reject) => { // return a promise so that you can handle it when you invoke `query`

        request(options, function (error, response) {
            if (error) {
              reject(new Error(error)); // reject instead of throwing, handle with `catch`
              return;
            }
            text = response.body;
            parser = new DOMParser();
            xmlDoc = parser.parseFromString(text, "text/xml");
            xmlResult = xmlDoc.getElementsByTagName(`${elementToParse}`)[0].childNodes[0].nodeValue;
            resolve(xmlResult); // resolve instead of returning, handle with `then`
        });
    })
}

query('Ticket', 'TicketNumber', 'BeginsWith', 'T2019', 'id')
    .then(xmlResult => console.log(xmlResult))
    .catch(err => /* do something with that `new Error(error)` you rejected in `query`*/);