#import // https://xhr.spec.whatwg.org/#interface-progressevent [Exposed=(Window,Worker)] interface ProgressEvent : Event { constructor(DOMString type, optional ProgressEventInit eventInitDict = {}); readonly attribute boolean lengthComputable; readonly attribute unsigned long long loaded; readonly attribute unsigned long long total; }; dictionary ProgressEventInit : EventInit { boolean lengthComputable = false; unsigned long loaded = 0; unsigned long total = 0; };