我想在我的AWS函数的main中返回一个值。我在从第一个回调中获取数据时遇到了麻烦,所以我可以将其发送到最后一个回调。
/** module used for outbound http requests */
var request = require('request');
/** module used for parsing XML easily. https://www.npmjs.com/package/xml2js*/
var parseString = require('xml2js').parseString;
exports.handler = (event, context, callback) => {
// testing array of coordinates
var arrayOfPoints = [39.7683800, -86.1580400, 41.881832, -87.623177];
var results = getXMLFromNOAA(arrayOfPoints);
callback(null, results); // <- returns 'undefined' in the AWS console. I'm assuming race condition.
};
/**
* getXMLFromNOAA
*
* This is a function used for figuring out the functionality of NOAA XML parsing
*
* @param arrayOfPoints {Array[Double]} - An evenly numbered index array of latitudes and longitudes
*
* @return result {XML/JSON} - weather information abled to be parsed
*/
function getXMLFromNOAA(arrayOfPoints, callback) {
var baseURL = "http://graphical.weather.gov/xml/sample_products/browser_interface/ndfdXMLclient.php?whichClient=NDFDgenLatLonList&lat=&lon=&listLatLon=";
// for-loop getting all points and dynamically adding them to the query url string
// iterate 2 at a time since they are coupled coordinates (e.g. [lat1, lng1, lat2, lng2, ... latN, lngN])
for(var i = 0; i < arrayOfPoints.length; i = i + 2)
{
// if we're at the end of the arrayOfPoints, finish up the chain of query coordinates
if( (i+2) == arrayOfPoints.length)
{
baseURL = baseURL.concat(arrayOfPoints[i]);
baseURL = baseURL.concat("%2C");
baseURL = baseURL.concat(arrayOfPoints[i+1]);
}
else
{
baseURL = baseURL.concat(arrayOfPoints[i]);
baseURL = baseURL.concat("%2C");
baseURL = baseURL.concat(arrayOfPoints[i+1]);
baseURL = baseURL.concat("+");
}
}
// TIME
baseURL = baseURL.concat("&lat1=&lon1=&lat2=&lon2=&resolutionSub=&listLat1=&listLon1=&listLat2=&listLon2=&resolutionList=&endPoint1Lat=&endPoint1Lon=&endPoint2Lat=&endPoint2Lon=&listEndPoint1Lat=&listEndPoint1Lon=&listEndPoint2Lat=&listEndPoint2Lon=&zipCodeList=&listZipCodeList=¢erPointLat=¢erPointLon=&distanceLat=&distanceLon=&resolutionSquare=&listCenterPointLat=&listCenterPointLon=&listDistanceLat=&listDistanceLon=&listResolutionSquare=&citiesLevel=&listCitiesLevel=§or=&gmlListLatLon=&featureType=&requestedTime=&startTime=&endTime=&compType=&propertyName=&product=time-series&begin=2016-09-04T00:00:00&end=2016-09-11T00:00:00");
// CHARACTERISTICS REQUESTED
// http://graphical.weather.gov/xml/docs/elementInputNames.php
baseURL = baseURL.concat("&Unit=e&maxt=maxt&mint=mint&temp=temp&appt=appt&rh=rh&sky=sky&wwa=wwa&iceaccum=iceaccum&ptornado=ptornado&phail=phail&ptstmwinds=ptstmwinds&pxtornado=pxtornado&pxhail=pxhail&ptotsvrtstm=ptotsvrtstm&wgust=wgust");
// Used for testing and seeing the final result
console.log(baseURL);
request(baseURL, function (error, response, body)
{
if (!error && response.statusCode == 200)
{
parseString(body, function (err, result) {
console.log('inside parseString: ' + result); // <- this prints but it won't show up in the main
// callback(null, result); <- doesnt work
return result; // doesnt work either
});
}
})
}
我希望能够使我的代码更模块化的可扩展性。我知道有一种方法可以采用getXMlFromNOAA
的异步过程并迭代地执行它们。我只是不太熟悉JavaScript。
您可以使用async模块使其更具可读性和灵活性,并且还可以避免异步问题。像这样写你的东西
/** module used for outbound http requests */
var request = require('request');
var async = require('async');
/** module used for parsing XML easily. https://www.npmjs.com/package/xml2js*/
var parseString = require('xml2js').parseString;
exports.handler = (event, context, callback) => {
async.waterfall([
function(next) {
// testing array of coordinates
var arrayOfPoints = [39.7683800, -86.1580400, 41.881832, -87.623177];
var results = getXMLFromNOAA(arrayOfPoints, next);
},
function(baseURL, next) {
request(baseURL, function(error, response, body) {
if (!error && response.statusCode == 200) {
parseString(body, function(err, result) {
console.log('inside parseString: ' + result); // <- this prints but it won't show up in the main
if (!err)
next(null, result);
});
}
})
}
], function(err, result) {
if (!err) {
callback(null, results); // <- returns 'undefined' in the AWS console. I'm assuming race condition.
}
})
};
/**
* getXMLFromNOAA
*
* This is a function used for figuring out the functionality of NOAA XML parsing
*
* @param arrayOfPoints {Array[Double]} - An evenly numbered index array of latitudes and longitudes
*
* @return result {XML/JSON} - weather information abled to be parsed
*/
function getXMLFromNOAA(arrayOfPoints, next) {
var baseURL = "http://graphical.weather.gov/xml/sample_products/browser_interface/ndfdXMLclient.php?whichClient=NDFDgenLatLonList&lat=&lon=&listLatLon=";
// for-loop getting all points and dynamically adding them to the query url string
// iterate 2 at a time since they are coupled coordinates (e.g. [lat1, lng1, lat2, lng2, ... latN, lngN])
for (var i = 0; i < arrayOfPoints.length; i = i + 2) {
// if we're at the end of the arrayOfPoints, finish up the chain of query coordinates
if ((i + 2) == arrayOfPoints.length) {
baseURL = baseURL.concat(arrayOfPoints[i]);
baseURL = baseURL.concat("%2C");
baseURL = baseURL.concat(arrayOfPoints[i + 1]);
} else {
baseURL = baseURL.concat(arrayOfPoints[i]);
baseURL = baseURL.concat("%2C");
baseURL = baseURL.concat(arrayOfPoints[i + 1]);
baseURL = baseURL.concat("+");
}
}
// TIME
baseURL = baseURL.concat("&lat1=&lon1=&lat2=&lon2=&resolutionSub=&listLat1=&listLon1=&listLat2=&listLon2=&resolutionList=&endPoint1Lat=&endPoint1Lon=&endPoint2Lat=&endPoint2Lon=&listEndPoint1Lat=&listEndPoint1Lon=&listEndPoint2Lat=&listEndPoint2Lon=&zipCodeList=&listZipCodeList=¢erPointLat=¢erPointLon=&distanceLat=&distanceLon=&resolutionSquare=&listCenterPointLat=&listCenterPointLon=&listDistanceLat=&listDistanceLon=&listResolutionSquare=&citiesLevel=&listCitiesLevel=§or=&gmlListLatLon=&featureType=&requestedTime=&startTime=&endTime=&compType=&propertyName=&product=time-series&begin=2016-09-04T00:00:00&end=2016-09-11T00:00:00");
// CHARACTERISTICS REQUESTED
// http://graphical.weather.gov/xml/docs/elementInputNames.php
baseURL = baseURL.concat("&Unit=e&maxt=maxt&mint=mint&temp=temp&appt=appt&rh=rh&sky=sky&wwa=wwa&iceaccum=iceaccum&ptornado=ptornado&phail=phail&ptstmwinds=ptstmwinds&pxtornado=pxtornado&pxhail=pxhail&ptotsvrtstm=ptotsvrtstm&wgust=wgust");
// Used for testing and seeing the final result
console.log(baseURL);
//retun to callback after getting URL
next(null, baseURL)
}
这不是回调的工作方式。将处理程序更改为如下内容:
exports.handler = (event, context, callback) => {
var arrayOfPoints = [39.7683800, -86.1580400, 41.881832, -87.623177];
getXMLFromNOAA(arrayOfPoints, function(result) {
console.log('returned');
console.log(result);
callback(null, result);
});
};
也取消注释(返回)到getXMLFromNOAA
中的callback(result)
;
NOAA也有一个模块。在重新发明轮子之前,一定要先搜索node-modules/npmjs.com/npms.io。这里的示例https://github.com/thataustin/noaa-forecasts与您正在做的非常相似,所以我将从它开始。
如果你想在未来简化异步的东西,你可以使用babel
与async
和await
关键字。但是你需要确保你首先真正学会了回调和承诺。