将 http 请求返回值保存在变量中

Question

I try to get data by using http request and callback function but i get undefined when i try to print the variable.

function httpGetAsync(theUrl, callback)
{
    var xmlHttp = new XMLHttpRequest();
    xmlHttp.onreadystatechange = function() { 
        if (xmlHttp.readyState == 4 && xmlHttp.status == 200)
            callback(xmlHttp.responseText);
    }
    xmlHttp.open("GET", theUrl, true);
    xmlHttp.send(null);
}

var response;
httpGetAsync("https://localhost:44319/api/Food/Get",function(result){
    response = result;
})

console.log(response)

Answer 1

Try put console.log(response) inside callback. Right now console.log is called before http response was received.