I'm trying to make a script that will return a respond when data is received on the current page. (New Data Received > Log its content to the console)
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (xhr.readyState == XMLHttpRequest.DONE) {
console.log(xhr.responseText);
}
}
xhr.prototype.open = (function(fopen){
return function(){
console.log("Data received.");
return fopen.apply(this,arguments);
}
})(XMLHttpRequest.prototype.open);
The above script is this script. (source)
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (xhr.readyState == XMLHttpRequest.DONE) {
console.log(xhr.responseText);
}
}
xhr.open('GET', 'http://example.com', true);
xhr.send(null);
Combine with this script. (source)
XMLHttpRequest.prototype.open = (function(fopen){
return function(){
console.log("Data received.");
return fopen.apply(this,arguments);
}
})(XMLHttpRequest.prototype.open)
I wanted to know what I did wrong and how to make it work. Thanks!
You're assigning to the prototype property of your instantiated object, not to the prototype of XMLHttpRequest. You might want to change XMLHttpRequest.prototype.onreadystatechange instead:
Object.defineProperty(XMLHttpRequest.prototype, 'onreadystatechange', {
set: function(listenerFn) {
this.addEventListener('readystatechange', function(...handlerArgs) {
if (this.readyState == XMLHttpRequest.DONE) {
// Custom action:
// console.log(xhr.responseText);
console.log('Detected a new response');
// Run the previous callback that was passed in:
listenerFn.apply(this, handlerArgs);
}
});
}
});
const xhr = new XMLHttpRequest();
xhr.open('GET', 'https://stacksnippets.net');
xhr.onreadystatechange = () => console.log('handler running');
xhr.send();
This isn't completely in line with the spec of course, this is just an example monkeypatch one might start with. (Mutating the built-in objects like XMLHttpRequest.prototype is bad practice, though - consider avoiding it if possible)
This will log all xhr request
XMLHttpRequest.prototype.send = (function(fsend){
return function(){
this.addEventListener('load', function(){
console.log("Data received.", this.response)
}, {once: true})
return fsend.apply(this, arguments);
}
})(XMLHttpRequest.prototype.send);
xhr = new XMLHttpRequest
xhr.open('GET', 'https://httpbin.org/get')
xhr.send()
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);
}
hi after searching in the net about how to use the long polling in JavaScript I ended up with three ways, they are mentioned here briefly,but they are implemented using JQuery. I am confused which one to use in case that the AJAX request that I send to the server is asynchronous GET request ,and I don't know how many time it could take.
here is an example AJAX request:
function asynchGETRequest(method,url){
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
console.log("ok");
}
};
xhttp.open(method, url, true);
xhttp.send();
return (xhttp.responseText);
}
var clientFunctions={
getAnswers : function(callback){
var res=asynchGETRequest("GET", "http://localhost:9000/answers");
callback(JSON.stringify(res));
}
}
clientFunctions.getAnswers (function(){
//do some code here after the ajax request is ended
});
can some one guide me please?
I think I found the solution here
function loadFile(sUrl, timeout, callback){
var args = arguments.slice(3);
var xhr = new XMLHttpRequest();
xhr.ontimeout = function () {
console.error("The request for " + url + " timed out.");
};
xhr.onload = function() {
if (xhr.readyState === 4) {
if (xhr.status === 200) {
callback.apply(xhr, args);
} else {
console.error(xhr.statusText);
}
}
};
xhr.open("GET", url, true);
xhr.timeout = timeout;
xhr.send(null);
}
Is it possible for me to call a function then override the contents of the variable before actually running it?
So I have a function that basically pulls in my Git profile like this:
var GetGitInfo = function() {
var xhr = new XMLHttpRequest();
var gitURL = "https://api.github.com/users/myself/repos";
xhr.open("GET", gitURL);
xhr.send(null);
xhr.onreadystatechange = function() {
var DONE = 4; // readyState 4 means the request is done.
var OK = 200; // status 200 is a successful return.
if (xhr.readyState === DONE) {
if (xhr.status === OK) {
// console.log(xhr.responseText);
console.log(JSON.parse(xhr.responseText));
} else {
console.log('Error: ' + xhr.status);
}
}
};
}
Then I call the function in another step by doing GetGitInfo(); which all works fine.
However, If I wanted to call the function and replace the gitURL variable how would I achieve that?
So something like
GetGitInfo(
gotURL= "https://api.github.com/users/new_user/repo";
);
You can't modify a local variable to a function from outside the function. They are private to the function's implementation.
But, since it's your own function, you can just create an argument that can be passed into the function. You can even make the argument optional so it will take your initial value as the default value if it is not passed.
var GetGitInfo = function(url) {
var xhr = new XMLHttpRequest();
var gitURL = url || "https://api.github.com/users/myself/repos";
xhr.open("GET", gitURL);
xhr.send(null);
xhr.onreadystatechange = function() {
var DONE = 4; // readyState 4 means the request is done.
var OK = 200; // status 200 is a successful return.
if (xhr.readyState === DONE) {
if (xhr.status === OK) {
// console.log(xhr.responseText);
console.log(JSON.parse(xhr.responseText));
} else {
console.log('Error: ' + xhr.status);
}
}
};
}
Then, you can use the function the way you were using it or you can pass in an URL to use:
getGitInfo(); // uses your default URL
getGitInfo("http://someURL"); // uses the URL you pass in
FYI, this function looks like it will ultimately need to either return a promise or accept a callback so you can communicate the results back to the caller.
From the snippet above you need to set the url as a function parameter so when calling it uses the specified url.
var GetInfo = function(url) {
var xhr = new XMLHttpRequest();
xhr.open("GET", url);
xhr.send(null);
xhr.onreadystatechange = function() {
var DONE = 4; // readyState 4 means the request is done.
var OK = 200; // status 200 is a successful return.
if (xhr.readyState === DONE) {
if (xhr.status === OK) {
// console.log(xhr.responseText);
console.log(JSON.parse(xhr.responseText));
} else {
console.log('Error: ' + xhr.status);
}
}
};
GetInfo("https://api.github.com/users/myself/repos");
You should do a toString() on the function:
GetGitInfo.toString()
Then you should do a text search and replace on the variable and it's data:
GetGitInfo.toString().substring(0,GetGitInfo.indexOf('somestring'))+'gitUrl="newURL"'+GetGitInfo.toString().substring(.......)
Then you should eval that string!
Or, you know, use function parameters. Either way. Whatever's easiest.
Pass a parameter to the function:
var GetGitInfo = function(gitURL) {
var xhr = new XMLHttpRequest();
xhr.open("GET", gitURL);
xhr.send(null);
xhr.onreadystatechange = function() {
var DONE = 4; // readyState 4 means the request is done.
var OK = 200; // status 200 is a successful return.
if (xhr.readyState === DONE) {
if (xhr.status === OK) {
// console.log(xhr.responseText);
console.log(JSON.parse(xhr.responseText));
} else {
console.log('Error: ' + xhr.status);
}
}
};
}
GetGetInfo("https://api.github.com/users/myself/repos");
Just add a parameter to your function:
var GetGitInfo = function(gitURL) {
var xhr = new XMLHttpRequest();
xhr.open("GET", gitURL);
xhr.send(null);
xhr.onreadystatechange = function() {
var DONE = 4; // readyState 4 means the request is done.
var OK = 200; // status 200 is a successful return.
if (xhr.readyState === DONE) {
if (xhr.status === OK) {
// console.log(xhr.responseText);
console.log(JSON.parse(xhr.responseText));
} else {
console.log('Error: ' + xhr.status);
}
}
};
}
and call it like this:
GetGitInfo("https://api.github.com/users/myself/repos");
Use the parameters
var getData = function(url){
// url can be used here
}
var data = getData("http://apiurl.xy")
I've got a problem with this Ajax code, is returning 0 everytime I access 'readyState'. Don't know what the source of the problem is yet, any help would be appreciated:
var xhr = null;
function performAjax(inputUrl){
// instantiate XMLHttpRequest object
try{
xhr = new XMLHttpRequest();
alert("XMLHttpRequest");
}
catch(e){
xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
// handle old browsers
if( xhr == null ) {
alert("Ajax not supported by your browser");
return;
}
// get the URL
var url = inputUrl;
alert(inputUrl);
// get Ajax answer
xhr.onreadystatechange = handler();
//alert(xhr.readyState);
xhr.open("POST", url, true);
xhr.send(null);
}
function handler() {
alert("Handler: " + xhr.readyState + " Status: " + xhr.status);
// handle only loaded requests
if(xhr.readyState == 4) { // state 4: that data has been received
alert("here");
if(xhr.status == 200) {
alert(xhr.reponseText);
}
else alert("Error with Ajax");
}
}
You're assigning the handler function incorrectly:
xhr.onreadystatechange = handler; // <--- THERE SHOULD BE NO PARENTHESES
When you include the parentheses, you're asking that the function be called. Without them, you're merely referring to the function, which is what you want.
I am trying to call an ajax request to my server for json data using a function. If I console out the resp variable inside the ajax function it will show the data successfully. If i try to set the ajax function to a variable, and then console that variable it returns undefined. Any ideas who to make the function request the data and then set ti to a variable to be consoled?
function jsonData(URL) {
var xhr = new XMLHttpRequest();
xhr.open("GET", URL, true);
xhr.onreadystatechange = function() {
if (xhr.readyState == 4) {
var resp = JSON.parse(xhr.responseText);
return resp;
}
}
xhr.send();
}
jsonString = jsonData(http://mywebsite.com/test.php?data=test);
console.log(jsonString);
This is actually pretty simple.. Change your call to by synchronous..
xhr.open("GET", URL, false);
That being said this will block the browser until the operation has been completed and if you can use a callback instead it would likely be preferred.
function jsonData(URL, cb) {
var xhr = new XMLHttpRequest();
xhr.open("GET", URL, true);
xhr.onreadystatechange = function() {
if (xhr.readyState == 4) {
var resp = JSON.parse(xhr.responseText);
cb(resp);
}
}
xhr.send();
}
jsonData("http://mywebsite.com/test.php?data=test"
, function(data) { console.log(data); });