try catch 不适用于 sse

Question

This is the code, PS: the service httpd in s10 is stopped

        try {
            var source = new EventSource("http://s10/server.php");
            console.log(source);
        } catch (e) {
            console.log("ADSfasfasfasdfasdfas" + e)
        }

this is the console:

why the heck the try catch is not catching the error ??

ofcourse I have onerror event and onclose event:

        source.addEventListener('error', function(e) {
            if (source.readyState == 2) {
                connectionClosed();//to change some style
                console.log("Disconnected");
            }

        }, false);

        source.onerror = function(e) {
            if (source.readyState != 0) {
                connectionClosed();//to change some style
                console.log("Disconnected");
            }
        };
        source.onclose = function() {
            connectionClosed();//to change some style
            console.log('Connection closed');
        }

Answer 1

When I run this in the Console on an arbitrary URL that isn't set up to handle SourceEvents, the Console successfully logs a SourceEvent instance. This is similar to what you're describing.

So my guess here is that there's no error to catch. The SourceEvent instance is successfully constructed, even though there's no actual connection. If you want to detect if the connection is working, use the EventSource.readyState property.

In my screenshot you can see that readyState = 0 , which means that the connection is "connecting", but in reality it's never going to finish connecting because the server on the other side isn't set up to handle SourceEvents.

https://developer.mozilla.org/en-US/docs/Web/API/EventSource/readyState

Answer 2

I'm testing the same thing, the onerror doesn't provide really useful info. For example, if you shut down your server or if you send an empty response while your client is connected, you can't detect programmatically on the client side the specific cause, I can see that just inspecting the dev console.