New to js. I am developing a personal site which uses tribute.js to have an #mention feature. In my case, I need to retrieve the mention list from a remote server. The official document gives an example to implement it. The thing confusing me is the meaning of cb parameter which is not even defined in anywhere. Could anyone help to explain it?
{
//..other config options
// function retrieving an array of objects
values: function (text, cb) {
remoteSearch(text, users => cb(users));
},
lookup: 'name',
fillAttr: 'name'
}
// ajax
function remoteSearch(text, cb) {
var URL = "YOUR DATA ENDPOINT";
xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (xhr.readyState === 4) {
if (xhr.status === 200) {
var data = JSON.parse(xhr.responseText);
cb(data);
} else if (xhr.status === 403) {
cb([]);
}
}
};
xhr.open("GET", URL + "?q=" + text, true);
xhr.send();
}
Meaning is hiding in the title of your question, cb means callback :)
It gets called by the remoteSearch function which in its turn was called with cb parameter passed by the tribute.js engine.
Related
Imagine this function:
function myMainFunction() {
doSomeInitialStuff();
// more stuff..
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function () {
if (xhr.readyState == XMLHttpRequest.DONE) {
// Now that we know we received the result, we can do the heavy lifting here
if (xhr.status == 200) {
console.log("ready 200");
let result = JSON.parse(xhr.responseText);
doStuff(result);
// and much more stuff..
} else {
console.log("error", xhr.status);
return undefined;
}
}
};
xhr.open("GET", "http://example.com", true);
xhr.send(null);
}
This works fine, but it is impossible to test, and this function has become a monster.
So I'd like to refactor it, by separating all the different parts in their own unique functions.
The problem is, I do not know how to extract the XHR part and still keep it working.
I cannot use Promises nor asnyc/await and have to stick to using plain XHR.
What I'd normally do is to create a seperate async function for the ajax call (or the xhr in this case). Simply await it's result and go from there. Easy to separate. But I do not have the luxury of await or anything this time.
What I am trying to get at is something like this
function refactoredMyMainFunction() {
doSomeInitialStuff();
// more stuff..
let result = xhrFunction();
doStuff(result); // result would be undefined here, since I cannot wait for the xhr request to finish.
}
You can implement a callback-based API:
function myMainFunction() {
doSomeInitialStuff();
// more stuff..
xhrFunction(doStuff);
}
function xhrFunction(cb) {
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function () {
if (xhr.readyState == XMLHttpRequest.DONE) {
// Now that we know we received the result, we can do the heavy lifting here
if (xhr.status == 200) {
console.log("ready 200");
let result = JSON.parse(xhr.responseText);
cb(result);
// and much more stuff..
} else {
console.log("error", xhr.status);
return undefined;
}
}
};
xhr.open("GET", "http://example.com", true);
xhr.send(null);
}
Background
I am making a request every 5 seconds using XMLHttpRequest and I want to print my name when I receive the response.
To do this I am using onreadystatechange which allows me to define a callback function when I receive the answer.
Problem
To achieve this, I am using a class. When I first initiate the class I say my name immediately, and then I start a process using setTimeInterval to make a request every 5 seconds and see my name.
The problem is that I see my name the first time, but then I never see it again. The issue is that this seems to be in different context, and thus this.sayMyName() doesn't exist because it doesn't belong to the xhr object.
What I tried
To fix this I tried using scoping by following another StackOverflow question but unfortunately this remains undefined.
Code
class Cook {
constructor() {
// innitial call so we don't have to wait
//5 seconds until we see my name
this.getCookInfo();
setInterval(this.getCookInfo, 5000);
}
getCookInfo() {
var xhr = new XMLHttpRequest(),
method = "GET",
url = "https://best.cooks.in.the.world.org/";
xhr.open(method, url, true);
//Call a function when the state changes.
xhr.onreadystatechange = (self => {
return () => {
if (xhr.readyState == XMLHttpRequest.DONE && xhr.status == 200)
self.sayMyName();
};
})(this);
}
sayMyName() {
console.log("Heisenberg");
}
}
Questions:
Is there a way to fix this code without have to pass a context object to the setInterval function?
Note
Kudos++ for those of you who get my reference :P
bind the this.getCookInfo function to this
then you can rally simplify your code
class Cook {
constructor() {
// innitial call so we don't have to wait
//5 seconds until we see my name
this.getCookInfo();
setInterval(this.getCookInfo.bind(this), 5000);
}
getCookInfo() {
var xhr = new XMLHttpRequest(),
method = "GET",
url = "https://best.cooks.in.the.world.org/";
xhr.open(method, url, true);
//Call a function when the state changes.
// no need for self gymnastics any more
// using onload, no need to test reasyState either
xhr.onload = e => {
if (xhr.status == 200)
this.sayMyName();
};
// your code lacks one thing
xhr.send();
}
sayMyName() {
console.log("Heisenberg");
}
}
An alternative -
class Cook {
constructor() {
this.getCookInfo();
}
getCookInfo() {
var getit = () => {
var xhr = new XMLHttpRequest(),
method = "GET",
url = "https://best.cooks.in.the.world.org/";
xhr.open(method, url, true);
//Call a function when the state changes.
xhr.onload = e => {
if (xhr.readyState == XMLHttpRequest.DONE && xhr.status == 200)
this.sayMyName();
};
xhr.send();
};
getit();
setInterval(getit, 5000);
}
sayMyName() {
console.log("Heisenberg");
}
}
I'm only 99% sure this is right though :p
Hello I've been trying to wrap my head around returning data from a XMLHttpRequest Function. I've tried many different ways but the only thing i can get when i try to output the data to a console from out-side the function i always get 'undefined'. it only works if i do it from inside the function itself.
<script>
var object;
function loadJSON(path, success, error) {
var xhr = new XMLHttpRequest();
var obj1;
xhr.onreadystatechange = function () {
if (xhr.readyState === XMLHttpRequest.DONE) {
if (xhr.status === 200) {
if (success)
success(JSON.parse(xhr.responseText));
//console.log(data); works here!
} else {
if (error)
error(xhr);
}
}
};
xhr.open("GET", path, true);
xhr.send();
}
object = loadJSON('jconfig.json',
function (data) { console.log(data); return($data);/*works here! but does not return!*/ },
function (xhr) { console.error(xhr); }
);
console.log(object);//does not work here
</script>
I know this is a very simple problem but I've been stuck with this problem for over an hour now and the answers given on other similar questions cant seem to get me over this obstacle. Any help is highly appreciated!
EDIT: I updated the code with some suggestions but i still cant get ti to work. Any suggestions to get the code above to finally return something i can use outside of the functions.
The line console.log(object) is executed just after the laodJSON() function is called and the JSON object isn't loaded till then.
This is related to callbacks and async functions. Your loadJSON() can only actually load the JSON when it get's response from the server.
Instead, if you want to call the JSON object outside the loadJSON() function, you need to use a callback function. Something like this:
<script>
var object;
function loadJSON(path, callback) {
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function () {
if (xhr.readyState === XMLHttpRequest.DONE) {
if (xhr.status === 200) {
// Here the callback gets implemented
object = JSON.parse(xhr.responseText);
callback();
} else {
}
}
};
xhr.open("GET", path, true);
xhr.send();
return xhr.onreadystatechange();
}
loadJSON('jconfig.json', function printJSONObject(){
console.log(object);
});
// this will not work unless you get the response
console.log(object);
</script>
Update: "Returning" a value from an async function by the use of callbacks is pointless, since the next line of code will be executed immediately without waiting for the response.
Instead, if you want to use the object outside of the function sending an XHR request, implement everything inside your callback function.
I have this code to make an ajax request, but according to Chrome Inspector the callback associated with the request is being called twice (by this I mean the response is being logged into the console twice), 2 more logs are being printed without any content. Here's the code:
var ajax = {
pull: function (settings) {
settings.type = 'get';
settings.callback = typeof (settings.callback) === 'function' ? settings.callback : false;
settings.data = settings.data ? settings.data : null;
return this.request(settings.url, settings.type, settings.callback, settings.data);
},
request: function (url, type, callback, data) {
var ids = ['MSXML2.XMLHTTP.3.0',
'MSXML2.XMLHTTP',
'Microsoft.XMLHTTP'],
xhr;
if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
} else {
for (var i = 0; i < ids.length; i++) {
try {
xhr = new ActiveXObject(ids[i]);
break;
} catch (e) {}
}
}
if (callback) {
xhr.onreadystatechange = function () {
callback(xhr);
};
}
xhr.open(type, url, true);
if (type.toUpperCase() === 'GET') {
xhr.send();
} else if (type.toUpperCase() === 'POST') {
xhr.send(data);
}
}
}
ajax.pull({
url: 'http://localhost/my/twtools/scripts/ajax.php',
callback: function (xhr) {
console.log(xhr.response);
}
});
xhr.onreadystatechange has several steps (numbered from 0 top 4 I do believe something like 0 = uninitialized, 1 = starting etc, although I can't rember the exact names of the steps anymore, a quick google should find them), and each step is calling your callback. If I remember correctly, the last stage is 4, so I do believe you need to check something like this
if (xhr.readyState == 4 && xhr.status == 200)
{
// call has finished successfully
}
inside you callback, i.e. to check that it is all finished and got a successful response
I've been spoilt by jQuery these days (so much easier to do with jQuery), been quite a while since I wrote raw ajax
You're using onreadystatechange, which gets called more than once (once each state change).
Try using
xhr.onload = function() {
callback(xhr);
};
I need to submit the a form using Ajax with POST method.The code is as follows,
function persistPage(divID,url,method){
var scriptId = "inlineScript_" + divID;
var xmlRequest = getXMLHttpRequest();
xmlRequest.open("POST",url,true);
xmlRequest.onreadystatechange = function(){
alert(xmlRequest.readyState + " :" + xmlRequest.status);
if (xmlRequest.readyState ==4 || xmlRequest.status == 200)
document.getElementById(divID).innerHTML=xmlRequest.responseText;
};
xmlRequest.open("POST", url, false);
alert(xmlRequest.readyState);
xmlRequest.send(null);
}
but the form is not submitting(request is not executed or no data posted).How to submit the form using Ajax.
Thanks
There's a few reasons why your code doesn't work. Allow me to break it down and go over the issues one by one. I'll start of with the last (but biggest) problem:
xmlRequest.send(null);
My guess is, you've based your code on a GET example, where the send method is called with null, or even undefined as a parameter (xhr.send()). This is because the url contains the data in a GET request (.php?param1=val1¶m2=val2...). When using post, you're going to have to pass the data to the send method.
But Let's not get ahead of ourselves:
function persistPage(divID,url,method)
{
var scriptId = "inlineScript_" + divID;
var xmlRequest = getXMLHttpRequest();//be advised, older IE's don't support this
xmlRequest.open("POST",url,true);
//Set additional headers:
xmlRequest.setRequestHeader('X-Requested-With', 'XMLHttpRequest');//marks ajax request
xmlRequest.setRequestHeader('Content-type', 'application/x-www-form-urlencode');//sending form
The first of the two headers is not always a necessity, but it's better to be safe than sorry, IMO. Now, onward:
xmlRequest.onreadystatechange = function()
{
alert(xmlRequest.readyState + " :" + xmlRequest.status);
if (xmlRequest.readyState ==4 || xmlRequest.status == 200)
document.getElementById(divID).innerHTML=xmlRequest.responseText;
};
This code has a number of issues. You're assigning a method to an object, so there's no need to refer to your object using xmlRequest, though technically valid here, this will break once you move the callback function outside the persistPage function. The xmlRequest variable is local to the function's scope, and cannot be accessed outside it. Besides, as I said before, it's a method: this points to the object directlyYour if statement is a bit weird, too: the readystate must be 4, and status == 200, not or. So:
xmlRequest.onreadystatechange = function()
{
alert(this.readyState + " :" + this.status);
if (this.readyState === 4 && this.status === 200)
{
document.getElementById(divID).innerHTML=this.responseText;
}
};
xmlRequest.open("POST", url, false);
alert(xmlRequest.readyState);//pointless --> ajax is async, so it will alert 0, I think
xmlRequest.send(data);//<-- data goes here
}
How you fill the data is up to you, but make sure the format matches the header: in this case 'content type','x-www-form-urlencode'. Here's a full example of just such a request, it's not exactly a world beater, since I was in the process of ditching jQ in favour of pure JS at the time, but it's serviceable and you might pick up a thing or two. Especially take a closer look at function ajax() definition. In it you'll see a X-browser way to create an xhr-object, and there's a function in there to stringify forms, too
POINTLESS UPDATE:
Just for completeness sake, I'll add a full example:
function getXhr()
{
try
{
return XMLHttpRequest();
}
catch (error)
{
try
{
return new ActiveXObject('Msxml2.XMLHTTP');
}
catch(error)
{
try
{
return new ActiveXObject('Microsoft.XMLHTTP');
}
catch(error)
{
//throw new Error('no Ajax support?');
alert('You have a hopelessly outdated browser');
location.href = 'http://www.mozilla.org/en-US/firefox/';
}
}
}
}
function formalizeObject(form)
{//we'll use this to create our send-data
recursion = recursion || false;
if (typeof form !== 'object')
{
throw new Error('no object provided');
}
var ret = '';
form = form.elements || form;//double check for elements node-list
for (var i=0;i<form.length;i++)
{
if (form[i].type === 'checkbox' || form[i].type === 'radio')
{
if (form[i].checked)
{
ret += (ret.length ? '&' : '') + form[i].name + '=' + form[i].value;
}
continue;
}
ret += (ret.length ? '&' : '') + form[i].name +'='+ form[i].value;
}
return encodeURI(ret);
}
function persistPage(divID,url,method)
{
var scriptId = "inlineScript_" + divID;
var xmlRequest = getXhr();
xmlRequest.open("POST",url,true);
xmlRequest.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
xmlRequest.setRequestHeader('Content-type', 'application/x-www-form-urlencode');
xmlRequest.onreadystatechange = function()
{
alert(this.readyState + " :" + this.status);
if (this.readyState === 4 && this.status === 200)
{
document.getElementById(divID).innerHTML=this.responseText;
}
};
xmlRequest.open("POST", url, false);
alert(xmlRequest.readyState);
xmlRequest.send(formalizeObject(document.getElementById('formId').elements));
}
Just for fun: this code, untested, but should work allright. Though, on each request the persistPage will create a new function object and assign it to the onreadystate event of xmlRequest. You could write this code so that you'll only need to create 1 function. I'm not going into my beloved closures right now (I think you have enough on your plate with this), but it's important to know that functions are objects, and have properties, just like everything else:Replace:
xmlRequest.onreadystatechange = function()
{
alert(this.readyState + " :" + this.status);
if (this.readyState === 4 && this.status === 200)
{
document.getElementById(divID).innerHTML=this.responseText;
}
};
With this:
//inside persistPage function:
xmlRequest.onreadystatechange = formSubmitSuccess;
formSubmitSuccess.divID = divID;//<== assign property to function
//global scope
function formSubmitSuccess()
{
if (this.readyState === 4 && this.status === 200)
{
console.log(this.responseText);
document.getElementById(formSubmitSuccess.divID).innerHTML = this.responseText;
//^^ uses property, set in persistPAge function
}
}
Don't use this though, as async calls could still be running while you're reassigning the property, causing mayhem. If the id is always going to be the same, you can, though (but closures would be even better, then).
Ok, I'll leave it at that
This code can let you understand. The function SendRequest send the request and build the xmlRequest through the GetXMLHttpRequest function
function SendRequest() {
var xmlRequest = GetXMLHttpRequest(),
if(xmlRequest) {
xmlRequest.open("POST", '/urlToPost', true)
xmlRequest.setRequestHeader("connection", "close");
xmlRequest.onreadystatechange = function() {
if (xmlRequest.status == 200) {
// Success
}
else {
// Some errors occured
}
};
xmlRequest.send(null);
}
}
function GetXMLHttpRequest() {
if (navigator.userAgent.indexOf("MSIE") != (-1)) {
var theClass = "Msxml2.XMLHTTP";
if (navigator.appVersion.indexOf("MSIE 5.5") != (-1)) {
theClass = "Microsoft.XMLHTTP";
}
try {
objectXMLHTTP = new ActivexObject(theClass);
return objectXMLHTTP;
}
catch (e) {
alert("Errore: the Activex will not be executed!");
}
}
else if (navigator.userAgent.indexOf("Mozilla") != (-1)) {
objectXMLHTTP = new XMLHttpRequest();
return objectXMLHTTP;
}
else {
alert("!Browser not supported!");
}
}
take a look at this page. In this line: req.send(postData); post data is an array with values that should be posted to server. You have null there. so nothing is posted. You just call request and send no data. In your case you must collect all values from your form, as XMLHTTPRequest is not something that can simply submit form. You must pass all values with JS:
var postData = {};
postData.value1 = document.getElementById("value1id").value;
...
xmlRequest.send(postData);
Where value1 will be available on server like $_POST['value'] (in PHP)
Also there might be a problem with URL or how you are calling persistPage. persistPage code looks ok to me, but maybe I'm missing something. Also you can take a look if you have no errors in console. Press F12 in any browser and find console tab. In FF you may need to install Firebug extention. Also there you will have Network tab with all requests. Open Firebug/Web Inspector(Chrome)/Developer Toolbar(IE) and check if new request is registered in its network tab after you call persistPage.
I found you've invoked the
xmlRequest.open()
method twice, one with async param as true and the other as false. What exactly do you intend to do?
xmlRequest.open("POST", url, true);
...
xmlRequest.open("POST", url, false);
If you want to send asynchronous request, pls pass the param as true.
And also, to use 'POST' method, you'd better send the request header as suggested by Elias,
xmlRequest.setRequestHeader('Content-type', 'application/x-www-form-urlencode');
Otherwise, you may still get unexpected issues.
If you want a synchronous request, actually you may handle the response directly right after you send the request, just like:
xmlRequest.open("POST", url, false);
xmlRequest.send(postData);
// handle response here
document.getElementById(scriptId).innerHTML = xmlRequest.responseText;
Hope this helps.