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Detect JSON exist

I have question about chechking file exists.
I have this piece of code.
function fileExists(url) {
if (url) {
var req = new XMLHttpRequest();
req.open('GET', url, false);
req.send();
console.log("exists");
return true;
} else {
console.log("no exists");
return false;
}
}
But it says me that file is exists. But it doesn't exists. In fact on my URL is 404 error XML file. Is possible somehow detect if requested URL is JSON? I need to return true only if checked file is JSON.
Thank you

Since this is a synchronous request, you can just try to parse the responseText you get back and if it fails to parse, you know it's not JSON:
var res = req.responseText;
try {
res = JSON.parse(res);
console.log('json', res);
} catch (e) {
console.log('not json')
}
If it were not a synchronous request, this would work:
If you look at the XMLHttpRequest docs, you'll see that in order to receive data back from an XMLHttpRequest, you need to add a callback function:
xhr.onreadystatechange = function() {//Call a function when the state changes.
if(this.readyState == XMLHttpRequest.DONE && this.status == 200) {
// Request finished. Do processing here.
}
}
If you wanted to check if your request is JSON, you could do this:
xhr.onreadystatechange = function() {//Call a function when the state changes.
if(this.readyState == XMLHttpRequest.DONE && this.status == 200) {
var res = this.responseText;
try {
JSON.parse(res);
console.log('json', res);
} catch (e) {
console.log('not json')
}
}
}

AJAX for reuse with different data? (NO jQuery) [duplicate]

How can I make an AJAX call using JavaScript, without using jQuery?

With "vanilla" (plain) JavaScript:
function loadXMLDoc() {
var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == XMLHttpRequest.DONE) { // XMLHttpRequest.DONE == 4
if (xmlhttp.status == 200) {
document.getElementById("myDiv").innerHTML = xmlhttp.responseText;
}
else if (xmlhttp.status == 400) {
alert('There was an error 400');
}
else {
alert('something else other than 200 was returned');
}
}
};
xmlhttp.open("GET", "ajax_info.txt", true);
xmlhttp.send();
}
With jQuery:
$.ajax({
url: "test.html",
context: document.body,
success: function() {
$(this).addClass("done");
}
});

Using the following snippet you can do similar things pretty easily, like this:
ajax.get('/test.php', {foo: 'bar'}, function() {});
Here is the snippet:
var ajax = {};
ajax.x = function () {
if (typeof XMLHttpRequest !== 'undefined') {
return new XMLHttpRequest();
}
var versions = [
"MSXML2.XmlHttp.6.0",
"MSXML2.XmlHttp.5.0",
"MSXML2.XmlHttp.4.0",
"MSXML2.XmlHttp.3.0",
"MSXML2.XmlHttp.2.0",
"Microsoft.XmlHttp"
];
var xhr;
for (var i = 0; i < versions.length; i++) {
try {
xhr = new ActiveXObject(versions[i]);
break;
} catch (e) {
}
}
return xhr;
};
ajax.send = function (url, callback, method, data, async) {
if (async === undefined) {
async = true;
}
var x = ajax.x();
x.open(method, url, async);
x.onreadystatechange = function () {
if (x.readyState == 4) {
callback(x.responseText)
}
};
if (method == 'POST') {
x.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
}
x.send(data)
};
ajax.get = function (url, data, callback, async) {
var query = [];
for (var key in data) {
query.push(encodeURIComponent(key) + '=' + encodeURIComponent(data[key]));
}
ajax.send(url + (query.length ? '?' + query.join('&') : ''), callback, 'GET', null, async)
};
ajax.post = function (url, data, callback, async) {
var query = [];
for (var key in data) {
query.push(encodeURIComponent(key) + '=' + encodeURIComponent(data[key]));
}
ajax.send(url, callback, 'POST', query.join('&'), async)
};

There is now a nicer Fetch API available natively in modern browsers. The fetch() method allows you to make web requests.
For example, to request some JSON from /get-data:
let options = {
method: 'GET',
headers: {}
};
fetch('/get-data', options)
.then(response => response.json())
.then(body => {
// Do something with body
});
See MDN Web Docs: Using the Fetch API for more details.

You can use the following function:
function callAjax(url, callback){
var xmlhttp;
// compatible with IE7+, Firefox, Chrome, Opera, Safari
xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function(){
if (xmlhttp.readyState == 4 && xmlhttp.status == 200){
callback(xmlhttp.responseText);
}
}
xmlhttp.open("GET", url, true);
xmlhttp.send();
}
You can try similar solutions online on these links:
https://www.w3schools.com/xml/tryit.asp?filename=tryajax_first
https://www.w3schools.com/xml/tryit.asp?filename=tryajax_callback

xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
alert(this.responseText);
}
};
xhttp.open("GET", "ajax_info.txt", true);
xhttp.send();

How about this version in plain ES6/ES2015?
function get(url) {
return new Promise((resolve, reject) => {
const req = new XMLHttpRequest();
req.open('GET', url);
req.onload = () => req.status === 200 ? resolve(req.response) : reject(Error(req.statusText));
req.onerror = (e) => reject(Error(`Network Error: ${e}`));
req.send();
});
}
The function returns a promise. Here is an example on how to use the function and handle the promise it returns:
get('foo.txt')
.then((data) => {
// Do stuff with data, if foo.txt was successfully loaded.
})
.catch((err) => {
// Do stuff on error...
});
If you need to load a json file you can use JSON.parse() to convert the loaded data into an JS Object.
You can also integrate req.responseType='json' into the function but unfortunately there is no IE support for it, so I would stick with JSON.parse().

Use XMLHttpRequest.
Simple GET request
httpRequest = new XMLHttpRequest()
httpRequest.open('GET', 'http://www.example.org/some.file')
httpRequest.send()
Simple POST request
httpRequest = new XMLHttpRequest()
httpRequest.open('POST', 'http://www.example.org/some/endpoint')
httpRequest.send('some data')
We can specify that the request should be asynchronous(true), the default, or synchronous(false) with an optional third argument.
// Make a synchronous GET request
httpRequest.open('GET', 'http://www.example.org/some.file', false)
We can set headers before calling httpRequest.send()
httpRequest.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
We can handle the response by setting httpRequest.onreadystatechange to a function before calling httpRequest.send()
httpRequest.onreadystatechange = function(){
// Process the server response here.
if (httpRequest.readyState === XMLHttpRequest.DONE) {
if (httpRequest.status === 200) {
alert(httpRequest.responseText);
} else {
alert('There was a problem with the request.');
}
}
}

You can get the correct object according to the browser with
function getXmlDoc() {
var xmlDoc;
if (window.XMLHttpRequest) {
// code for IE7+, Firefox, Chrome, Opera, Safari
xmlDoc = new XMLHttpRequest();
}
else {
// code for IE6, IE5
xmlDoc = new ActiveXObject("Microsoft.XMLHTTP");
}
return xmlDoc;
}
With the correct object, a GET might can be abstracted to:
function myGet(url, callback) {
var xmlDoc = getXmlDoc();
xmlDoc.open('GET', url, true);
xmlDoc.onreadystatechange = function() {
if (xmlDoc.readyState === 4 && xmlDoc.status === 200) {
callback(xmlDoc);
}
}
xmlDoc.send();
}
And a POST to:
function myPost(url, data, callback) {
var xmlDoc = getXmlDoc();
xmlDoc.open('POST', url, true);
xmlDoc.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xmlDoc.onreadystatechange = function() {
if (xmlDoc.readyState === 4 && xmlDoc.status === 200) {
callback(xmlDoc);
}
}
xmlDoc.send(data);
}

I was looking for a way to include promises with ajax and exclude jQuery. There's an article on HTML5 Rocks that talks about ES6 promises. (You could polyfill with a promise library like Q) You can use the code snippet that I copied from the article.
function get(url) {
// Return a new promise.
return new Promise(function(resolve, reject) {
// Do the usual XHR stuff
var req = new XMLHttpRequest();
req.open('GET', url);
req.onload = function() {
// This is called even on 404 etc
// so check the status
if (req.status == 200) {
// Resolve the promise with the response text
resolve(req.response);
}
else {
// Otherwise reject with the status text
// which will hopefully be a meaningful error
reject(Error(req.statusText));
}
};
// Handle network errors
req.onerror = function() {
reject(Error("Network Error"));
};
// Make the request
req.send();
});
}
Note: I also wrote an article about this.

A small combination from a couple of the examples below and created this simple piece:
function ajax(url, method, data, async)
{
method = typeof method !== 'undefined' ? method : 'GET';
async = typeof async !== 'undefined' ? async : false;
if (window.XMLHttpRequest)
{
var xhReq = new XMLHttpRequest();
}
else
{
var xhReq = new ActiveXObject("Microsoft.XMLHTTP");
}
if (method == 'POST')
{
xhReq.open(method, url, async);
xhReq.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xhReq.setRequestHeader("X-Requested-With", "XMLHttpRequest");
xhReq.send(data);
}
else
{
if(typeof data !== 'undefined' && data !== null)
{
url = url+'?'+data;
}
xhReq.open(method, url, async);
xhReq.setRequestHeader("X-Requested-With", "XMLHttpRequest");
xhReq.send(null);
}
//var serverResponse = xhReq.responseText;
//alert(serverResponse);
}
// Example usage below (using a string query):
ajax('http://www.google.com');
ajax('http://www.google.com', 'POST', 'q=test');
OR if your parameters are object(s) - minor additional code adjustment:
var parameters = {
q: 'test'
}
var query = [];
for (var key in parameters)
{
query.push(encodeURIComponent(key) + '=' + encodeURIComponent(parameters[key]));
}
ajax('http://www.google.com', 'POST', query.join('&'));
Both should be fully browser + version compatible.

If you don't want to include JQuery, I'd try out some lightweight AJAX libraries.
My favorite is reqwest. It's only 3.4kb and very well built out: https://github.com/ded/Reqwest
Here's a sample GET request with reqwest:
reqwest({
url: url,
method: 'GET',
type: 'json',
success: onSuccess
});
Now if you want something even more lightweight, I'd try microAjax at a mere 0.4kb: https://code.google.com/p/microajax/
This is all the code right here:
function microAjax(B,A){this.bindFunction=function(E,D){return function(){return E.apply(D,[D])}};this.stateChange=function(D){if(this.request.readyState==4){this.callbackFunction(this.request.responseText)}};this.getRequest=function(){if(window.ActiveXObject){return new ActiveXObject("Microsoft.XMLHTTP")}else{if(window.XMLHttpRequest){return new XMLHttpRequest()}}return false};this.postBody=(arguments[2]||"");this.callbackFunction=A;this.url=B;this.request=this.getRequest();if(this.request){var C=this.request;C.onreadystatechange=this.bindFunction(this.stateChange,this);if(this.postBody!==""){C.open("POST",B,true);C.setRequestHeader("X-Requested-With","XMLHttpRequest");C.setRequestHeader("Content-type","application/x-www-form-urlencoded");C.setRequestHeader("Connection","close")}else{C.open("GET",B,true)}C.send(this.postBody)}};
And here's a sample call:
microAjax(url, onSuccess);

XMLHttpRequest()
You can use the XMLHttpRequest() constructor to create a new XMLHttpRequest (XHR) object which will allow you to interact with a server using standard HTTP request methods (such as GET and POST):
const data = JSON.stringify({
example_1: 123,
example_2: 'Hello, world!',
});
const request = new XMLHttpRequest();
request.addEventListener('load', function () {
if (this.readyState === 4 && this.status === 200) {
console.log(this.responseText);
}
});
request.open('POST', 'example.php', true);
request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
request.send(data);
fetch()
You can also use the fetch() method to obtain a Promise which resolves to the Response object representing the response to your request:
const data = JSON.stringify({
example_1: 123,
example_2: 'Hello, world!',
});
fetch('example.php', {
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8',
},
body: data,
}).then(response => {
if (response.ok) {
response.text().then(response => {
console.log(response);
});
}
});
navigator.sendBeacon()
On the other hand, if you are simply attempting to POST data and do not need a response from the server, the shortest solution would be to use navigator.sendBeacon():
const data = JSON.stringify({
example_1: 123,
example_2: 'Hello, world!',
});
navigator.sendBeacon('example.php', data);

Try using the Fetch Api (Fetch API)
fetch('http://example.com/movies.json').then(response => response.json()).then(data => console.log(data));
Its really clear, and 100% vanilla.

Old but I will try, maybe someone will find this info useful.
This is the minimal amount of code you need to do a GET request and fetch some JSON formatted data. This is applicable only to modern browsers like latest versions of Chrome, FF, Safari, Opera and Microsoft Edge.
const xhr = new XMLHttpRequest();
xhr.open('GET', 'https://example.com/data.json'); // by default async
xhr.responseType = 'json'; // in which format you expect the response to be
xhr.onload = function() {
if(this.status == 200) {// onload called even on 404 etc so check the status
console.log(this.response); // No need for JSON.parse()
}
};
xhr.onerror = function() {
// error
};
xhr.send();
Also check out new Fetch API which is a promise-based replacement for XMLHttpRequest API.

From youMightNotNeedJquery.com + JSON.stringify
var request = new XMLHttpRequest();
request.open('POST', '/my/url', true);
request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
request.send(JSON.stringify(data));

This may help:
function doAjax(url, callback) {
var xmlhttp = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject("Microsoft.XMLHTTP");
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
callback(xmlhttp.responseText);
}
}
xmlhttp.open("GET", url, true);
xmlhttp.send();
}

<html>
<script>
var xmlDoc = null ;
function load() {
if (typeof window.ActiveXObject != 'undefined' ) {
xmlDoc = new ActiveXObject("Microsoft.XMLHTTP");
xmlDoc.onreadystatechange = process ;
}
else {
xmlDoc = new XMLHttpRequest();
xmlDoc.onload = process ;
}
xmlDoc.open( "GET", "background.html", true );
xmlDoc.send( null );
}
function process() {
if ( xmlDoc.readyState != 4 ) return ;
document.getElementById("output").value = xmlDoc.responseText ;
}
function empty() {
document.getElementById("output").value = '<empty>' ;
}
</script>
<body>
<textarea id="output" cols='70' rows='40'><empty></textarea>
<br></br>
<button onclick="load()">Load</button>
<button onclick="empty()">Clear</button>
</body>
</html>

Well it is just a 4 step easy proceess,
I hope it helps
Step 1. Store the reference to the XMLHttpRequest object
var xmlHttp = createXmlHttpRequestObject();
Step 2. Retrieve the XMLHttpRequest object
function createXmlHttpRequestObject() {
// will store the reference to the XMLHttpRequest object
var xmlHttp;
// if running Internet Explorer
if (window.ActiveXObject) {
try {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {
xmlHttp = false;
}
}
// if running Mozilla or other browsers
else {
try {
xmlHttp = new XMLHttpRequest();
} catch (e) {
xmlHttp = false;
}
}
// return the created object or display an error message
if (!xmlHttp)
alert("Error creating the XMLHttpRequest object.");
else
return xmlHttp;
}
Step 3. Make asynchronous HTTP request using the XMLHttpRequest object
function process() {
// proceed only if the xmlHttp object isn't busy
if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0) {
// retrieve the name typed by the user on the form
item = encodeURIComponent(document.getElementById("input_item").value);
// execute the your_file.php page from the server
xmlHttp.open("GET", "your_file.php?item=" + item, true);
// define the method to handle server responses
xmlHttp.onreadystatechange = handleServerResponse;
// make the server request
xmlHttp.send(null);
}
}
Step 4. Executed automatically when a message is received from the server
function handleServerResponse() {
// move forward only if the transaction has completed
if (xmlHttp.readyState == 4) {
// status of 200 indicates the transaction completed successfully
if (xmlHttp.status == 200) {
// extract the XML retrieved from the server
xmlResponse = xmlHttp.responseText;
document.getElementById("put_response").innerHTML = xmlResponse;
// restart sequence
}
// a HTTP status different than 200 signals an error
else {
alert("There was a problem accessing the server: " + xmlHttp.statusText);
}
}
}

in plain JavaScript in the browser:
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (xhr.readyState == XMLHttpRequest.DONE ) {
if(xhr.status == 200){
console.log(xhr.responseText);
} else if(xhr.status == 400) {
console.log('There was an error 400');
} else {
console.log('something else other than 200 was returned');
}
}
}
xhr.open("GET", "mock_data.json", true);
xhr.send();
Or if you want to use Browserify to bundle your modules up using node.js. You can use superagent:
var request = require('superagent');
var url = '/mock_data.json';
request
.get(url)
.end(function(err, res){
if (res.ok) {
console.log('yay got ' + JSON.stringify(res.body));
} else {
console.log('Oh no! error ' + res.text);
}
});

Here's a JSFiffle without JQuery
http://jsfiddle.net/rimian/jurwre07/
function loadXMLDoc() {
var xmlhttp = new XMLHttpRequest();
var url = 'http://echo.jsontest.com/key/value/one/two';
xmlhttp.onreadystatechange = function () {
if (xmlhttp.readyState == XMLHttpRequest.DONE) {
if (xmlhttp.status == 200) {
document.getElementById("myDiv").innerHTML = xmlhttp.responseText;
} else if (xmlhttp.status == 400) {
console.log('There was an error 400');
} else {
console.log('something else other than 200 was returned');
}
}
};
xmlhttp.open("GET", url, true);
xmlhttp.send();
};
loadXMLDoc();

var load_process = false;
function ajaxCall(param, response) {
if (load_process == true) {
return;
}
else
{
if (param.async == undefined) {
param.async = true;
}
if (param.async == false) {
load_process = true;
}
var xhr;
xhr = new XMLHttpRequest();
if (param.type != "GET") {
xhr.open(param.type, param.url, true);
if (param.processData != undefined && param.processData == false && param.contentType != undefined && param.contentType == false) {
}
else if (param.contentType != undefined || param.contentType == true) {
xhr.setRequestHeader('Content-Type', param.contentType);
}
else {
xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
}
}
else {
xhr.open(param.type, param.url + "?" + obj_param(param.data));
}
xhr.onprogress = function (loadTime) {
if (param.progress != undefined) {
param.progress({ loaded: loadTime.loaded }, "success");
}
}
xhr.ontimeout = function () {
this.abort();
param.success("timeout", "timeout");
load_process = false;
};
xhr.onerror = function () {
param.error(xhr.responseText, "error");
load_process = false;
};
xhr.onload = function () {
if (xhr.status === 200) {
if (param.dataType != undefined && param.dataType == "json") {
param.success(JSON.parse(xhr.responseText), "success");
}
else {
param.success(JSON.stringify(xhr.responseText), "success");
}
}
else if (xhr.status !== 200) {
param.error(xhr.responseText, "error");
}
load_process = false;
};
if (param.data != null || param.data != undefined) {
if (param.processData != undefined && param.processData == false && param.contentType != undefined && param.contentType == false) {
xhr.send(param.data);
}
else {
xhr.send(obj_param(param.data));
}
}
else {
xhr.send();
}
if (param.timeout != undefined) {
xhr.timeout = param.timeout;
}
else
{
xhr.timeout = 20000;
}
this.abort = function (response) {
if (XMLHttpRequest != null) {
xhr.abort();
load_process = false;
if (response != undefined) {
response({ status: "success" });
}
}
}
}
}
function obj_param(obj) {
var parts = [];
for (var key in obj) {
if (obj.hasOwnProperty(key)) {
parts.push(encodeURIComponent(key) + '=' + encodeURIComponent(obj[key]));
}
}
return parts.join('&');
}
my ajax call
var my_ajax_call=ajaxCall({
url: url,
type: method,
data: {data:value},
dataType: 'json',
async:false,//synchronous request. Default value is true
timeout:10000,//default timeout 20000
progress:function(loadTime,status)
{
console.log(loadTime);
},
success: function (result, status) {
console.log(result);
},
error :function(result,status)
{
console.log(result);
}
});
for abort previous requests
my_ajax_call.abort(function(result){
console.log(result);
});

HTML :
<!DOCTYPE html>
<html>
<head>
<script>
function loadXMLDoc()
{
var xmlhttp;
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","1.php?id=99freebies.blogspot.com",true);
xmlhttp.send();
}
</script>
</head>
<body>
<div id="myDiv"><h2>Let AJAX change this text</h2></div>
<button type="button" onclick="loadXMLDoc()">Change Content</button>
</body>
</html>
PHP:
<?php
$id = $_GET[id];
print "$id";
?>

A verry good solution with pure javascript is here
/*create an XMLHttpRequest object*/
let GethttpRequest=function(){
let httpRequest=false;
if(window.XMLHttpRequest){
httpRequest =new XMLHttpRequest();
if(httpRequest.overrideMimeType){
httpRequest.overrideMimeType('text/xml');
}
}else if(window.ActiveXObject){
try{httpRequest =new ActiveXObject("Msxml2.XMLHTTP");
}catch(e){
try{
httpRequest =new ActiveXObject("Microsoft.XMLHTTP");
}catch(e){}
}
}
if(!httpRequest){return 0;}
return httpRequest;
}
/*Defining a function to make the request every time when it is needed*/
function MakeRequest(){
let uriPost ="myURL";
let xhrPost =GethttpRequest();
let fdPost =new FormData();
let date =new Date();
/*data to be sent on server*/
let data = {
"name" :"name",
"lName" :"lName",
"phone" :"phone",
"key" :"key",
"password" :"date"
};
let JSONdata =JSON.stringify(data);
fdPost.append("data",JSONdata);
xhrPost.open("POST" ,uriPost, true);
xhrPost.timeout = 9000;/*the time you need to quit the request if it is not completed*/
xhrPost.onloadstart = function (){
/*do something*/
};
xhrPost.onload = function (){
/*do something*/
};
xhrPost.onloadend = function (){
/*do something*/
}
xhrPost.onprogress =function(){
/*do something*/
}
xhrPost.onreadystatechange =function(){
if(xhrPost.readyState < 4){
}else if(xhrPost.readyState === 4){
if(xhrPost.status === 200){
/*request succesfull*/
}else if(xhrPost.status !==200){
/*request failled*/
}
}
}
xhrPost.ontimeout = function (e){
/*you can stop the request*/
}
xhrPost.onerror = function (){
/*you can try again the request*/
};
xhrPost.onabort = function (){
/*you can try again the request*/
};
xhrPost.overrideMimeType("text/plain; charset=x-user-defined-binary");
xhrPost.setRequestHeader("Content-disposition", "form-data");
xhrPost.setRequestHeader("X-Requested-With","xmlhttprequest");
xhrPost.send(fdPost);
}
/*PHP side
<?php
//check if the variable $_POST["data"] exists isset() && !empty()
$data =$_POST["data"];
$decodedData =json_decode($_POST["data"]);
//show a single item from the form
echo $decodedData->name;
?>
*/
/*Usage*/
MakeRequest();

Fast code fetch without jQuery
async function product_serach(word) {
var response = await fetch('<?php echo base_url(); ?>home/product_search?search='+word);
var json = await response.json();
for (let [key, value] of Object.entries(json))
{
console.log(json)
}
}

Method in class not being called after XMLHttpRequest is done

I have the following method to log into my API:
login()
{
var formData = new FormData();
formData.append("admin[email]", "user");
formData.append("admin[password]", "pass");
var request = new XMLHttpRequest();
request.open("POST", "my_link");
request.onreadystatechange = (function() {
if (request.readyState === XMLHttpRequest.DONE && request.status === 201)
{
return function() { this.loadMembers(); }
}
});
request.send(formData);
}
Then I have my method that I'm trying to call AFTER my post async request is completely done:
loadMembers()
{
....
}
Now for some reason, this.loadMembers() is never being called. If I put a testing console.log() right above it (not within the return callback) it calls just fine - so I know that the requestState and request status is correct.
Is there a better way to do this? Or what am I doing wrong?
Thanks

It is because you are returning a function instead of just calling loadMembers.
So instead of:
request.onreadystatechange = (function() {
if (request.readyState === XMLHttpRequest.DONE && request.status === 201)
{
return function() { this.loadMembers(); }
}
});
You likely want:
var that = this;
request.onreadystatechange = (function() {
if (request.readyState === XMLHttpRequest.DONE && request.status === 201)
{
that.loadMembers();
}
});

Remember the "this" in login() is not the same this as the one inside the (function() { if....}) so you need to save this var that = this in the way that rasmeister shows.

Add EXTRA parameter to XMLHttpRequest Handler

Following is the way I know for adding parameters to request handlers for XMLHttpRequest.
var request = new XMLHttpRequest();
function ABC() {
if (request) {
request.open('GET', url, true);
request.onreadystatechange = function() { handler(param1, param2); };
request.send();
}
}
function handler(param1, param2) {
if (request.readyState == 4) {
if (request.status == 200) {
//do something on success
} else {
alert("Invocation Errors Occured");
}
}
}
That is fine and good. But, kindly look at the following code.
var request = new XMLHttpRequest();
function ABC() {
if (request) {
request.open('GET', url, true);
request.onreadystatechange = handler;
request.send();
}
}
function handler(evtXHR) {
if (request.readyState == 4) {
if (request.status == 200) {
//do something on success
} else {
alert("Invocation Errors Occured");
}
}
}
Here, i'm calling the handler without any parameter, but i'm getting an object of type XMLHttpRequestProgressEvent in the evtXHR parameter of the code.
Now I have two questions.
How am I getting evtXHR parameter when I make a parameter-less call?
How to add a parameter along with evtXHR so that I still get the XMLHttpRequestProgressEvent object?
So, I want something like this:
function handler(evtXHR, myParam) {
if (request.readyState == 4) {
if (request.status == 200) {
//do something on success
} else {
alert("Invocation Errors Occured");
}
}
}

You aren't making a call. the XHR object is. The handler function is being called by the XHR object in response to receiving the event.
Don't try to pass it as an argument. Use a closure instead.
Such:
var myData = 1234;
request.onreadystatechange = handler;
function handler(event) {
alert(myData); // Use myData from the wider scope instead of trying to pass it as an argument
}

How to make ajax failures visible?

I use a small library to make ajax calls. I want the function to throw an error if it is fed a url that does not exist.
Currently, it fails silently, and simply passes back undefined for the response text. This makes general trouble shooting more difficult.
Is there an easy way to do this?
/**************************************************************************************************
AJAX
*/
// specify type/url/callback in passed object
Pub.ajax = function (config_ajax) {
var xhr = new win.XMLHttpRequest();
// get
if (config_ajax.type === 'get') {
xhr.open('GET', config_ajax.url, true);
xhr.onload = function () {
if (this.status === 200) {
config_ajax.callback(xhr.responseText);
}
};
xhr.send(null);
}
// post
if (config_ajax.type === 'post') {
xhr.open("POST", config_ajax.url, true);
xhr.setRequestHeader("Content-type",
"application/x-www-form-urlencoded");
xhr.onload = function () {
if (this.status === 200) {
config_ajax.callback(xhr.responseText);
}
};
xhr.send(config_ajax.data);
}
// post for form_data
if (config_ajax.type === 'multi') {
xhr.open("POST", config_ajax.url, true);
xhr.onload = function () {
if (this.status === 200) {
config_ajax.callback(xhr.responseText);
}
};
xhr.send(config_ajax.data);
}
};

I'm assuming you can't use jQuery $.ajax which has an .success and .error.
You may need to make this a little more robust depending on what your calling and exactly how the server responds.
if (this.status === 200) {
config_ajax.callback(xhr.responseText);
} else if (console) {
console.error("ajax call failed"
}

try this
**************************************************************************************************
AJAX
*/
// specify type/url/callback in passed object
Pub.ajax = function (config_ajax) {
var xhr = new win.XMLHttpRequest();
// get
if (config_ajax.type === 'get') {
xhr.open('GET', config_ajax.url, true);
xhr.onload = function () {
if (this.status === 200) {
config_ajax.callback(xhr.responseText);
}
};
xhr.send(null);
}
// post
if (config_ajax.type === 'post') {
xhr.open("POST", config_ajax.url, true);
xhr.setRequestHeader("Content-type",
"application/x-www-form-urlencoded");
xhr.onload = function () {
if (this.status === 200) {
config_ajax.callback(xhr.responseText);
}
};
xhr.send(config_ajax.data);
}
// post for form_data
if (config_ajax.type === 'multi') {
xhr.open("POST", config_ajax.url, true);
xhr.onload = function () {
if (this.status === 200) {
config_ajax.callback(xhr.responseText);
}
};
xhr.send(config_ajax.data);
}
// when the ready state changes check for success or failure
xhr.onreadystatechange=function(){
if (xhr.readyState==4 && xhr.status==200)
{
//Success
alert('success');
}else{
//Failure
alert('Failure');
}
}
};