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    This article is in need of a technical review.

    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

    Document Tags and Contributors

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