Question

How do you make asynchronous HTTP request?

Answer 1

Browsers provide an XMLHttpRequest object which can be used to make asynchronous HTTP requests from JavaScript by passing the 3rd parameter as true.

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