JavaScript var 位于函数之外

Question

如何在 fn() 函数之外检索 returndata 变量？

function fn() {
    var xmlhttp = new XMLHttpRequest();
    var vars = "request=something";

    xmlhttp.open("POST", "script.php", true);
    xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

    xmlhttp.onreadystatechange = function() {
        if(xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            var returndata = xmlhttp.responseText;
        }
    }

    xmlhttp.send(vars);
}

Answer 1

您需要在函数之前定义全局变量，然后将结果存储到该变量中。现在的方法是定义局部变量。

var returndata;
function fn() {
    var xmlhttp = new XMLHttpRequest();
    var vars = "request=something";

    xmlhttp.open("POST", "script.php", true);
    xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

    xmlhttp.onreadystatechange = function() {
        if(xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            returndata = xmlhttp.responseText;
        }
    }

    xmlhttp.send(vars);
}