JavaScript XMLHttpReqsuest和全局变量问题

Question

出于某种原因，我在运行和编辑代码时不断遇到这两个错误。

请注意，我使用全局变量myArr。我一直在说：

  

＆＃34;错误myArr[j]未定义＆＃34;

每当我尝试解析函数内的数据时，选择事实＆＃34;或者从myArr返回parseJSONdata()，而不是：

  

＆＃34;错误XHLHttpRequest未定义＆＃34;。

var myArr= [];
function parseJSONdata() {
  //parse data
  var xmlhttp = new XMLHttpReqsuest();
  xmlhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      myArr = JSON.parse(this.responseText);
    }
  };
  xmlhttp.open("GET", "Fact.json", true);
  xmlhttp.send();
}


function ChooseFact() {
  // compare 
  for (let i = 0; i <bul.length; i++){
    if (i == key){
      var j = i;
    } 
  }

  return myArr[j].Fact;
}

这是我关注的代码部分。

以下是整个代码供参考。

var bul = [ {
"Building" : "CEER",
"Latitude" : 40.0366404,
"Longitude" : -75.3457346
}, {
"Building" : "Bartley",
"Latitude" : 40.034595,
"Longitude" : -75.3383853
}, {
"Building" : "Mendel",
"Latitude" : 40.0378151,
"Longitude" : -75.3419795
}, {
"Building" : "Falvey",
"Latitude" : 40.037469,
"Longitude" : -75.342546
} ];

var x = document.getElementById("demo");


function getLocation() {
if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(showPosition);
} else {
    x.innerHTML = "Geolocation is not supported by this browser.";
}
}
function showPosition(position) {
var latitude = position.coords.latitude;
var longitude = position.coords.longitude;
var w =NearestBuilding(latitude,longitude);
x.innerHTML = w; 
x.innerHTML = ChooseFact();

 }

function Deg2Rad(deg) {
return deg * Math.PI / 180;
}

function convertDistance(lat1, lon1, lat2, lon2) {
lat1 = Deg2Rad(lat1);
lat2 = Deg2Rad(lat2);
lon1 = Deg2Rad(lon1);
lon2 = Deg2Rad(lon2);
var R = 6371e3; // km
var x = (lon2 - lon1) * Math.cos((lat1 + lat2) / 2);
var y = (lat2 - lat1);
var d = Math.sqrt(x * x + y * y) * R;
return d;
}
var key; 

function NearestBuilding(latitude, longitude) {
var mindif = 999999;
var closest;

for (let i = 0; i < bul.length; i++) {
    var dif = convertDistance(latitude, longitude, bul[i].Latitude,
            bul[i].Longitude);
    console.log(i,dif);
    if (dif < mindif) {
        closest = i;
        mindif = dif;   
    }
}
//  if (dif<5){
key = closest;
return  bul[closest].Building;

//  }
//  else{
//  return "Error: Must be less than 15 feet away from a Building";
//    }
}

var myArr = [];

function parseJSONdata() {
//parse data
var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
     myArr = JSON.parse(this.responseText);
    }
};

xmlhttp.open("GET", "Fact.json", true);
xmlhttp.send();
return myArr;
}


function ChooseFact(){
// compare 
for (let i = 0; i <bul.length; i++){
    if (i == key){
        var j = i;} 
}
myArr= parseJSONdata();
return myArr[j].Fact;
}