FileReader: progress event

Note: This feature is available in Web Workers.

The progress event of the FileReader interface is fired periodically as the FileReader reads data.

This event is not cancelable and does not bubble.


Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener("progress", (event) => {});

onprogress = (event) => {};

Event type

Event properties

Also inherits properties from its parent Event.

ProgressEvent.lengthComputable Read only

A boolean flag indicating if the total work to be done, and the amount of work already done, by the underlying process is calculable. In other words, it tells if the progress is measurable or not.

ProgressEvent.loaded Read only

A 64-bit unsigned integer value indicating the amount of work already performed by the underlying process. The ratio of work done can be calculated by dividing total by the value of this property. When downloading a resource using HTTP, this only counts the body of the HTTP message, and doesn't include headers and other overhead. Read only

A 64-bit unsigned integer representing the total amount of work that the underlying process is in the progress of performing. When downloading a resource using HTTP, this is the Content-Length (the size of the body of the message), and doesn't include the headers and other overhead.


Live example


<div class="example">
  <div class="file-select">
    <label for="avatar">Choose a profile picture:</label>
      accept="image/png, image/jpeg" />

  <img src="" class="preview" height="200" alt="Image preview" />

  <div class="event-log">
    <label for="eventLog">Event log:</label>
    <textarea readonly class="event-log-contents" id="eventLog"></textarea>


const fileInput = document.querySelector('input[type="file"]');
const preview = document.querySelector("img.preview");
const eventLog = document.querySelector(".event-log-contents");
const reader = new FileReader();

function handleEvent(event) {
  eventLog.textContent += `${event.type}: ${event.loaded} bytes transferred\n`;

  if (event.type === "load") {
    preview.src = reader.result;

function addListeners(reader) {
  reader.addEventListener("loadstart", handleEvent);
  reader.addEventListener("load", handleEvent);
  reader.addEventListener("loadend", handleEvent);
  reader.addEventListener("progress", handleEvent);
  reader.addEventListener("error", handleEvent);
  reader.addEventListener("abort", handleEvent);

function handleSelected(e) {
  eventLog.textContent = "";
  const selectedFile = fileInput.files[0];
  if (selectedFile) {

fileInput.addEventListener("change", handleSelected);



File API
# dfn-progress-event
File API
# dfn-onprogress

Browser compatibility

BCD tables only load in the browser

See also