为什么500错误打破了ajax调用？

Question

This is my code:

http_request = new XMLHttpRequest();
if (http_request.overrideMimeType) http_request.overrideMimeType('text/javascript');
http_request.onreadystatechange = alertContents;
http_request.open('POST', base_url, true);
http_request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
http_request.setRequestHeader("Content-length", parameters.length);
http_request.setRequestHeader("Connection", "close");
http_request.send(parameters);

Being run in the latest firefox.

This code normally works perfectly, but when the page called produces a 500 internal server error javascript stops running on the page, and further events scheduled with setInterval/setInterval do not get executed. Why does this happen? How do I catch it?

Answer 1

The problem may be in your alertContents function (not shown in your question). A function called by .onreadystatechange almost always looks something like this:

var callback = function() {
  if (http_request.readyState==4 && http_request.status==200) {
    // do stuff
  }
}

if the page produces a 500 Http code then the if statement will fail and the rest of the code in the callback will not execute. To catch it add:

else if(http_request.readyState==4 && http_request.status==500) {
  console.log('The server\'s on fire!');
}