node.js - 方法在完成函数执行之前返回值

Question

function rip(intent_update, output_rnr){
    var headers_conv = {
        'Content-Type': 'application/json',
        'Accept': 'application/json',
        'Authorization': 'Basic YWFjZWU2M'
    };
    var dataString = '{ "output": { "text": {  "values": [' + output_rnr + '] }  }  }';
    var options_conv = {
        url: 'https://watson-api-explorer.mybluemix.net/'+ intent_update + '?version=2017-05-26',
        method: 'POST',
        headers: headers_conv,
        body: dataString
    };
    function callback_conv(error, response, body) {
        if (!error && response.statusCode === 200) {
            console.log(body);
        }
    }
    request(options_conv, callback_conv);
}
app.post('/api/message', function(req, res) {
  var workspace = process.env.WORKSPACE_ID || '<workspace-id>';
  }
  var payload = {
    workspace_id: workspace,
    context: req.body.context || {},
    input: req.body.input || {}
  };

  // Send the input to the conversation service
  conversation.message(payload, function(err, data) {
    if (err) {
      return res.status(err.code || 500).json(err);
    }
    return res.json(updateMessage(payload, data));
  });
});

function updateMessage(input, response) {
  if (!response.output) {
    response.output = {};
  } else {
    if (response.intents.length > 0 && (response.intents[0].intent === 'rnr')) {
            response = getCalculationResult(response);
    }

  }
   return response;
 }

function getCalculationResult(response){

    var result = '';
    if(response.intents[0].intent === 'rnr'){
        var question  = response.input.text;
        var query     = qs.stringify({q: question, ranker_id: ranker_id, fl: 'contentHtml'});

        solrClient.get('fcselect', query, function(err, searchResponse) {
            if(err) {
                 console.log('Error searching for documents: ' + err);
            }
            else {
                result = JSON.stringify(searchResponse.response.docs[0].contentHtml, null, 1);
                rip(response.intents[0].intent, result);
            }
        });

    }
    /*
     * if(result === ''){
            setTimeout(function(){
            response.output.text[0] = result + response.input.text;
        }, 15000);
    }
    else{
        var output = result + response.input.text;
        response.output.text[0] = output;
    }
    */
    response.output[0].text = response.output[0].text + result;
    return response;

}

此代码在完成方法执行之前从函数返回值。我尝试过使用 setTimeout 但结果仍然相同。如何重写我的方法以等到方法执行完成后再返回值。我也尝试过使用回调进行编写，但无法获得所需的结果(可能是我以错误的方式实现回调)

Answer 1

您可以使用 Promise.all，并用一段自定义代码说:“只要这些功能完成，那么，就执行此操作”。

例如...

var message = "";

promise1 = new Promise((resolve, reject) => {
    setTimeout(() => {
        message += "my";
        resolve(message);
    }, 2000)
})

promise2 = new Promise((resolve, reject) => {
    setTimeout(() => {
        message += " first";
        resolve(message);
    }, 2000)
})

promise3 = new Promise((resolve, reject) => {
    setTimeout(() => {
        message += " promise";
        resolve(message);
    }, 2000)
})

var printResult = (results) => {console.log("Results = ", results, "message = ", message)}

function main() {
    // See the order of promises. Final result will be according to it
    Promise.all([promise1, promise2, promise3]).then(printResult);
    Promise.all([promise2, promise1, promise3]).then(printResult);
    Promise.all([promise3, promise2, promise1]).then(printResult);
    console.log("\"\"" + message);
}

main();

查看官方documentation关于 Promise 在这里。

查看此tutorial通过有关 Promise 的示例来理解。