ProgressEvent

ProgressEvent()

Creates a ProgressEvent event with the given parameters.

Also inherits properties from its parent Event.

ProgressEvent.lengthComputable Read only

A boolean flag indicating if the ratio between the size of the data already transmitted or processed (loaded), and the total size of the data (total), is calculable. In other words, it tells if the progress is measurable or not.

ProgressEvent.loaded Read only

A 64-bit unsigned integer indicating the size, in bytes, of the data already transmitted or processed. The ratio can be calculated by dividing ProgressEvent.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. Note that for compressed requests of unknown total size, loaded might contain the size of the compressed, or decompressed, data, depending on the browser. As of 2024, it contains the size of the compressed data in Firefox, and the size of the uncompressed data in Chrome.

ProgressEvent.total Read only

A 64-bit unsigned integer indicating the total size, in bytes, of the data being transmitted or processed. When downloading a resource using HTTP, this value is taken from the Content-Length response header. It only counts the body of the HTTP message, and doesn't include headers and other overhead.

Inherits methods from its parent, Event.

The following example adds a ProgressEvent to a new XMLHTTPRequest and uses it to display the status of the request.

const progressBar = document.getElementById("p"),
  client = new XMLHttpRequest();
client.open("GET", "magical-unicorns");
client.onprogress = (pe) => {
  if (pe.lengthComputable) {
    progressBar.max = pe.total;
    progressBar.value = pe.loaded;
  }
};
client.onloadend = (pe) => {
  progressBar.value = pe.loaded;
};
client.send();

• The Event base interface.