Primary function proceeds while a vital component is still being generated. How do I make the function wait?

//Load npm modules
const express = require('express');
const bodyParser = require('body-parser');
const request = require('request');

//Set obj 'app' to express();
const app = express();

app.use(bodyParser.urlencoded({ extended: false}));

app.set('view engine', 'pug');

app.get('/', (req, res, next) => {
    res.render('index');
});

app.post('/lookup', (req, res, next) => {
    const battletag = req.body.battletag;
    console.log("running");
    var stats = lookupStats(battletag);
    console.log("lookupStats() completed. Attempting to render stats.");
    res.render(stats);
});

app.listen(3000, () => {
    console.log('The application is running on localhost:3000!')
});


function apiRequestObj(battletag) {
    var requestObj = {
        uri: "https://owapi.net/api/v3/u/" + battletag + "/blob?platform=pc",
        timeout: 10000,
        headers: {
            'User-Agent': 'Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.43 Safari/537.31'
        }
    }
    return requestObj;
}

function apiRequest(requestObj) {
    request(requestObj, function(err, res, body) {
        if (err) {
            return "Error: " + err;
        } else {
            var result = JSON.parse(body);
            result = result.us.stats.competitive.overall_stats;
            console.log(result);
            return result;
        }
    });
}

function lookupStats(battletag) {
    battletag = battletag.replace('#', '-');
    console.log("Searching Battletag: " + battletag);
    var requestObj = apiRequestObj(battletag);
    var apiResult = apiRequest(requestObj);
    console.log(apiResult);
    return apiResult;
}

The application is running on localhost:3000!
running
Searching Battletag: Unreal-11505
undefined
lookupStats() completed. Attempting to render stats.
TypeError: Path must be a string. Received undefined
    at assertPath (path.js:7:11)
    at extname (path.js:1431:5)
    at new View (/Users/neil/Dropbox/Programming/Web Development/owapi/node_modules/express/lib/view.js:56:14)
    at EventEmitter.render (/Users/neil/Dropbox/Programming/Web Development/owapi/node_modules/express/lib/application.js:570:12)
    at ServerResponse.render (/Users/neil/Dropbox/Programming/Web Development/owapi/node_modules/express/lib/response.js:1008:7)
    at app.post (/Users/neil/Dropbox/Programming/Web Development/owapi/app.js:22:9)
    at Layer.handle [as handle_request] (/Users/neil/Dropbox/Programming/Web Development/owapi/node_modules/express/lib/router/layer.js:95:5)
    at next (/Users/neil/Dropbox/Programming/Web Development/owapi/node_modules/express/lib/router/route.js:137:13)
    at Route.dispatch (/Users/neil/Dropbox/Programming/Web Development/owapi/node_modules/express/lib/router/route.js:112:3)
    at Layer.handle [as handle_request] (/Users/neil/Dropbox/Programming/Web Development/owapi/node_modules/express/lib/router/layer.js:95:5)
{ level: 61,
  comprank: 2031,
  games: 116,
  win_rate: 53.21,
  losses: 51,
  rank_image: 'https://d1u1mce87gyfbn.cloudfront.net/game/playerlevelrewards/0x0250000000000928_Border.png',
  wins: 58,
  ties: 7,
  prestige: 1,
  avatar: 'https://d1u1mce87gyfbn.cloudfront.net/game/unlocks/0x02500000000002F7.png',
  tier: 'gold' }