The ProgressEvent.lengthComputable read-only property is a Boolean flag indicating if the resource concerned by the ProgressEvent has a length that can be calculated. If not, the ProgressEvent.total property has no significant value.

API Progress Events ProgressEvent Property

The ProgressEvent interface represents events measuring progress of an underlying process, like an HTTP request (for an XMLHttpRequest, or the loading of the underlying resource of an <img>, <audio>, <video>, <style> or <link>).

API Interface Progress Events ProgressEvent Reference

The ProgressEvent.initProgressEvent() method Initializes an animation event created using the deprecated Document.createEvent("ProgressEvent") method.

API Deprecated Method Progress Events ProgressEvent