This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.


This property specifies a callback function to be run repeatedly while the operation represented by a FileRequest object is in progress.


instanceOfFileRequest.onprogress = function;

Where instanceOfFileRequest is a FileRequest object and function is the JavaScript function to execute.

Each time the function callback is called, it gets an object as its first parameter. Those objects contain two properties:

A number representing the current amount of bytes processed by the operation.
A number representing the total amount of bytes that will be processed by the operation.


// Assuming 'request' which is a FileRequest object

request.onprogress = function (status) {
  var progress = document.querySelector('progress');

  progress.value = status.loaded;
  progress.max   =;


Not part of any current specification.

See also

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 Contributors to this page: fscholz, kscarfone, Jeremie
 Last updated by: fscholz,