PROGRESS EVENTS

The Progress Events specification is a W3C Working Draft defining events for client-server communication. These events were first targeted at XHR explicitly but have now also made their way into other similar APIs. There are six progress events:

• loadstart—Fires when the first byte of the response has been received.
• progress—Fires repeatedly as a response is being received.
• error—Fires when there was an error attempting the request.
• abort—Fires when the connection was terminated by calling abort().
• load—Fires when the response has been fully received.
• loadend—Fires when the communication is complete and after firing error, abort, or load.

Each request begins with the loadstart event being fired; followed by one or more progress events; then one of error, abort, or load; finally ending with loadend.

Most of these events are straightforward, but there are two that have some subtleties to be aware of.

The load Event

When Firefox...