How to check the availability of a resource using JavaScript?

Question

If I have a URL to a video file, how can I detect if the resource pointed by the URL is valid and exists before it can be displayed? I've seen some answers suggesting AJAX, but I only know AJAX to send and retrieve some data, not to get the status of the file whether it exists or not.

For example, if I have a URL like http://www.example.com/video.mp4, how could I check whether video.mp4 exists or not and can or cannot be retrieved?

Answer 1

You can send a HEAD request. HEAD requests send back only the HTTP headers, so if you get a status of 200 or 304 it means the resource exists, if you get a 404 it means the resource doesn't exist.