How to implement AJAX request?

How to implement AJAX request?

1. Create an XMLHttpRequest instance;

var xhr;if(window.XMLHttpRequest) {
  //ie7+,firefox,chrome,safari,opera
  xhr = new XMLHttpRequest();}else {
  //ie5,ie6
  xhr = new ActiveXObject("Microsoft.XMLHTTP");}

2. Listen to the readystatechange event and determine the request status through the readyState attribute;

xhr.onreadystatechange = function() {
  if(xhr.readyState==4 && xhr.status==200) {
    console.log(xhr.responseText);
  }}

3. Call open() The method specifies the request type and address;

xhr.open("GET", "xhr_info.txt");

4. Just call the send() method to send the request.

xhr.send(null);

Complete code

var xhr;
if(window.XMLHttpRequest) {
  //ie7+,firefox,chrome,safari,opera
  xhr = new XMLHttpRequest();
} else {
  //ie5,ie6
  xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
xhr.onreadystatechange = function() {
  if(xhr.readyState==4 && xhr.status==200) {
    console.log(xhr.responseText);
  }
}
xhr.open("GET", "xhr_info.txt", true);
xhr.send(null);

Recommended tutorial: "JS Tutorial"

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