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Detecting if ajax call errored out due to either server down or network not there

Hi,
I am making an ajax call like :

$.ajax({
            type: 'POST',
            contentType: 'application/json',
            url: postURL,
            data: JSON.stringify(objectTobeSent),
            success: function(note, status, xhr) {
                
                
            },
            error: function(request, status, error) {
                var responseText = request.responseText;
                $('.error_message').text(responseText);
                $('.error_message').show();
            }
        });
    });

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I stopped the server that serves this request. And so when this ajax call was executed it errored out.
I found that in such cases request.readyState value is 0. But unsure whether this is always the case.

will putting a check for this is fine if i want to detect that there was some problem establishing connection ?
Also on https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/readyState
it states that UNSENT means that client has been created and open() is not yet called.
what happens when open() is called and why in case of internet not there or server is down its throwing readyState as 0 ? why cannt it call open ?? does open establishes a connection with the server ? and state is sent to OPENED only when the connection is established properly ?

Thanks

Swatantra Bhargava

By calling $.post that way, you automatically pass only in a success handler function.

If something on the request went wrong, this method is not even executed.

To have more control either use $.ajax() directly, or pass in fail handlers. That could look like

$.post("page.php", {data: stuff}, function(data, status) {
// we're fine here
}).fail(function(err, status) {
// something went wrong, check err and status
});
The same thing using .ajax():

$.ajax({
type: 'POST',
url: 'page.php',
data: stuff,
success: function( data ) {
},
error: function(xhr, status, error) {
// check status && error
},
dataType: 'text'
});

Rohit Bajaj

ASKER

I am using $.ajax here . I want to understand what each readyState means

ASKER CERTIFIED SOLUTION

Swatantra Bhargava

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