Node.js 无法使用 JSON 数据读取未定义的属性

Question

I'm trying to convert a js script to a node.js script. The JS script works fine, and managed to pull data from this URL and correctly use the information. However, when I try run it on Node.js, I get the error "Cannot read property of 'fixtures' undefined." I've added this package to pull the data, however I'm not sure why it's now throwing an error.

var XMLHttpRequest = require("xmlhttprequest").XMLHttpRequest;
var xhr = new XMLHttpRequest();

//Get Data
var getJSON = function(url, callback) {
    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.responseType = 'json';
    xhr.onload = function() {
        var status = xhr.status;
        if (status === 200) {
        callback(null, xhr.response);
        } else {
        callback(status, xhr.response);
        }
    };
    xhr.send();
};

//Use Data
getJSON('http://api.football-data.org/v1/teams/343/fixtures',
function(err, data) {
    if (err !== null) {
    console.log("   An error has occured.")
    } else {
    var latest;
    for(x = 0; data.fixtures[x].status !== "TIMED"; x++) {
        latest = data.fixtures[x].matchday - 1;
    }
}};

The error is thrown at the line while(data.fixtures[x].status !== "TIMED") , and the error is

for(x = 0; data.fixtures[x].status !== "TIMED"; x++) {
               ^

TypeError: Cannot read property 'fixtures' of undefined

Please could you explain to me why JS can see the data and use it fine, but node.js sees the property to be undefined?

Many thanks.

EDIT: Removed legacy while loop that shouldn't have been there.

Answer 1

The response property is part XMLHttpRequest Level 2 , but xmlhttprequest only supports 1 at the moment:

Note: This library currently conforms to XMLHttpRequest 1.

For this reason xhr.response will be undefined .

Only xhr.responseText will be set, and this is a string so you would need to add the parsing of json yourself.

if (status === 200) {
  try { // use a try block here in case the the response is not parseable
     callback(null, JSON.parse(xhr.responseText));
  } catch(e) {
     callback(e)
  }
} else {

  callback(status, xhr.response);
}

Answer 2

The reason you're getting that message is because the variable data in your callback is undefined . The reason it is so is that you are passing it that

callback(null, xhr.response); //<-- You should have used responseText

But even that will not solve the issue - it is text not json. So parse it

callback(null, JSON.parse(xhr.responseText));