FileSystemObserver: FileSystemObserver() constructor

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

Non-standard: This feature is not standardized. We do not recommend using non-standard features in production, as they have limited browser support, and may change or be removed. However, they can be a suitable alternative in specific cases where no standard option exists.

The FileSystemObserver() constructor creates a new FileSystemObserver object instance.

Syntax

new FileSystemObserver(callback)

Parameters

callback

A user-defined callback function that will be called when the observer has observed a change in the file system entry it has been asked to observe (via FileSystemObserver.observe()). The callback function will be passed the following two parameters:

records: An array of FileSystemChangeRecord objects that contain details of all the observed changes.
observer: A reference to the current FileSystemObserver object, which is made available in case, for example, you want to stop observations after the current records have been received using the FileSystemObserver.disconnect() method.

Return value

A new FileSystemObserver object.

Examples

Note: For a complete working example, check out File System Observer Demo (source code).

Initializing a `FileSystemObserver`

Before you can start observing file or directory changes, you need to initialize a FileSystemObserver to handle the observations:

const observer = new FileSystemObserver(callback);

The callback function body can be specified to return and process file change observations in any way you want:

const callback = (records, observer) => {
  for (const record of records) {
    console.log("Change detected:", record);
    const reportContent = `Change observed to ${record.changedHandle.kind} ${record.changedHandle.name}. Type: ${record.type}.`;
    sendReport(reportContent); // Some kind of user-defined reporting function
  }

  observer.disconnect();
};

Specifications

Not currently part of a specification. See https://github.com/whatwg/fs/pull/165 for the relevant specification PR.