What sort of situations could cause this handler to be called? I'm not finding any instance where this method throws an error.
I tried with the device offline, I get xmlHttpRequest.status = 0
but no error.
Question is what sort of situations can I create in order to test functionality of this handler.
var xmlhttp = new XMLHttpRequest(),
method = 'GET',
url = 'https://developer.mozilla.org/';
xmlhttp.open(method, url, true);
xmlhttp.onerror = function () {
console.log("** An error occurred during the transaction");
};
xmlhttp.send();
From: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequestEventTarget/onerror
XMLHttpRequest (XHR) objects are used to interact with servers. You can retrieve data from a URL without having to do a full page refresh. This enables a Web page to update just part of a page without disrupting what the user is doing. XMLHttpRequest is used heavily in AJAX programming.
To send an HTTP request, create an XMLHttpRequest object, open a URL, and send the request. After the transaction completes, the object will contain useful information such as the response body and the HTTP status of the result.
How do I fix the XHR error? Technically, this is not error, it is normal response. The message tells you that you just tried to enter a secure room without the key, your error is that you don't have the key/authorization to enter that room. The only solution is to get the key/credentials and include on the request.
Your question is the perfect example. Just try your code from your web developer console while on this very page.
Here, try it yourself:
var xmlhttp = new XMLHttpRequest(),
method = 'GET',
url = 'https://developer.mozilla.org/';
xmlhttp.open(method, url, true);
xmlhttp.onerror = function () {
console.log("** An error occurred during the transaction");
};
xmlhttp.send();
When dealing with any network based IO all kinds of things could happen. Cross-Origin requests are only one. What if the server is offline, DNS lookup fails, a router between you and the server that is critical point of failure goes down?
Since an XHR call is for a server response, onerror would come into play when there is an error at the server. Changing your client to be offline doesn't simulate a server error.
Suppose the server resource gets moved and the server responds with a 404 error? What if the server times out? What if the request itself is malformed and causes the server to throw an error?
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