如何修复TypeError：undefined不是对象错误？

Question

I'm trying to add results of a file got using XMLHttpRequest to an array. The file is a json.

Here's a Code that creates the error:

var array = [];
var req = new XMLHttpRequest();
req("get", "test.json");
req.onreadystatechange = handle(req, array);
req.send();

function handle(req, array) {
    if ((req.target.readyState == 4) && (req.target.status == 200)) {
        var json = JSON.parse(req.target.responseText);
        array.push(json.test);
        alert(array);

    }
}

Without using target is has the value 4

Answer 1

You have used wrong property of request.

Try with inline function for onreadystatechange callback

var array = [];
var req = new XMLHttpRequest();
req("get", "test.json");
req.onreadystatechange = function(){
     if ((req.readyState == 4) && (req.status == 200)) {
        var json = JSON.parse(req.responseText);
        array.push(json.test);
        alert(array);
    }
};
req.send();

or as per your way

var array = [];
    var req = new XMLHttpRequest();
    req("get", "test.json");
    req.onreadystatechange = handle();
    req.send();
function handle(){
         if ((req.readyState == 4) && (req.status == 200)) {
            var json = JSON.parse(req.responseText);
            array.push(json.test);
            alert(array);
        }
    };