JavaScript AJAX Add an AJAX preloader
Example
Here's a way to show a GIF preloader while an AJAX call is executing. We need to prepare our add and remove preloader functions:
function addPreloader() {
// if the preloader doesn't already exist, add one to the page
if(!document.querySelector('#preloader')) {
var preloaderHTML = '<img id="preloader" src="https://goo.gl/cNhyvX" />';
document.querySelector('body').innerHTML += preloaderHTML;
}
}
function removePreloader() {
// select the preloader element
var preloader = document.querySelector('#preloader');
// if it exists, remove it from the page
if(preloader) {
preloader.remove();
}
}
Now we're going to look at where to use these functions.
var request = new XMLHttpRequest();
Inside the onreadystatechange function you should have an if statement with condition: request.readyState == 4 && request.status == 200.
If true: the request is finished and response is ready that's where we'll use removePreloader().
Else if false: the request is still in progress, in this case we'll run the function addPreloader()
xmlhttp.onreadystatechange = function() {
if(request.readyState == 4 && request.status == 200) {
// the request has come to an end, remove the preloader
removePreloader();
} else {
// the request isn't finished, add the preloader
addPreloader()
}
};
xmlhttp.open('GET', your_file.php, true);
xmlhttp.send();
