XMLHttpRequest.timeout

The XMLHttpRequest.timeout property is an unsigned long representing the number of milliseconds a request can take before automatically being terminated. The default value is 0, which means there is no timeout. Timeout shouldn't be used for synchronous XMLHttpRequests requests used in a document environment or it will throw an InvalidAccessError exception. When a timeout happens, a timeout event is fired.

Note: You may not use a timeout for synchronous requests with an owning window.

Using a timeout with an asynchronous request 

In Internet Explorer, the timeout property may be set only after calling the open() method and before calling the send() method.

Example

var xhr = new XMLHttpRequest();
xhr.open('GET', '/server', true);
xhr.timeout = 2000; // time in milliseconds
xhr.onload = function () {
  // Request finished. Do processing here.
};
xhr.ontimeout = function (e) {
  // XMLHttpRequest timed out. Do something here.
};
xhr.send(null);

Specifications