Node.js：REST调用和请求函数返回未定义的值

Question

I have been trying to learn the MEAN stack and ran into some issues with the javascript below that is in node.js. I have been having trouble with my module.exports.homelist function in which the functions, like function (err, response, body), have been giving me those values as undefined. I have been searching for answers for a while and came across asynchronous code and the callback function, but I was unable to find the solution that fits my situation, especially when the function is called on from within a request.

The Code:

var request = require('request');
var apiOptions = {
    server : "https://localhost:3000"
};
if (process.env.NODE_ENV === 'production') {
    apiOptions.server = "https://getting-mean-loc8r.herokuapp.com";
}

var renderHomepage = function (req, res, responseBody) {
    var message;
    if (!(responseBody instanceof Array)) {
        message = "API lookup error";
        responseBody = [];
    } else {
        if (!responseBody.length) {
            message = "No places found nearby";
        }
    }
    res.render('locations-list', {
        title: 'Loc8r - find a place to work with wifi',
        pageHeader: {
            title: 'Loc8r',
            strapline: 'Find places to work with wifi near you!'
        },
        sidebar: "Looking for wifi and a seat? Loc8r helps you find places to work when out and about. Perhaps with coffee, cake or a pint? Let Loc8r help you find the place you're looking for.",
        locations: responseBody,
        message: message
    });
}

/* GET 'home' page */
module.exports.homelist = function(req, res) {
    var requestOptions, path;
    path = '/api/locations';
    requestOptions = {
        url : apiOptions.server + path,
        method : "GET",
        json : {},
        qs : {
            lng : -0.7992599,
            lat : 51.378091,
            maxDistance : 20
        }
    };
    request(
        requestOptions,
        function(err, response, body) {
            var i, data;
            data = body;
            if (data !== undefined && response !== undefined && response.statusCode === 200 && data.length) {
                for (i=0; i<data.length; i++) {
                    data[i].distance = _formatDistance(data[i].distance);
                }
            }
            renderHomepage(req, res, data);
        }
    );

    var _formatDistance = function (distance) {
        var numDistance, unit;
        if (distance > 1) {
            numDistance = parseFloat(distance).toFixed(1);
            unit = 'km';
        } else {
            numDistance = parseInt(distance * 1000,10);
            unit = 'm';
        }
        return numDistance + unit;
    }
};

EDIT: This is the code I have in another file that uses my homelist function to render an HTML homepage:

var express = require('express'); var router = express.Router(); 
var ctrlLocations = require('../controllers/locations');
router.get('/', ctrlLocations.homelist);
module.exports = router;

Answer 1

You mention MEAN stack- are you requiring express? Please read the documentation on the express website.