W3cubDocs

FileReader

The FileReader object lets web applications asynchronously read the contents of files (or raw data buffers) stored on the user's computer, using File or Blob objects to specify the file or data to read.

File objects may be obtained from a FileList object returned as a result of a user selecting files using the <input> element, from a drag and drop operation's DataTransfer object, or from the mozGetAsFile() API on an HTMLCanvasElement.

Note: This feature is available in Web Workers.

Constructor

FileReader(): Returns a newly constructed FileReader.

See Using files from web applications for details and examples.

Properties

FileReader.error Read only

A DOMException representing the error that occurred while reading the file.

FileReader.readyState Read only

A number indicating the state of the FileReader. This is one of the following:

`EMPTY`	`0`	No data has been loaded yet.
`LOADING`	`1`	Data is currently being loaded.
`DONE`	`2`	The entire read request has been completed.

FileReader.result Read only

The file's contents. This property is only valid after the read operation is complete, and the format of the data depends on which of the methods was used to initiate the read operation.

Event handlers

FileReader.onabort: A handler for the abort event. This event is triggered each time the reading operation is aborted.
FileReader.onerror: A handler for the error event. This event is triggered each time the reading operation encounter an error.
FileReader.onload: A handler for the load event. This event is triggered each time the reading operation is successfully completed.
FileReader.onloadstart: A handler for the loadstart event. This event is triggered each time the reading is starting.
FileReader.onloadend: A handler for the loadend event. This event is triggered each time the reading operation is completed (either in success or failure).
FileReader.onprogress: A handler for the progress event. This event is triggered while reading a Blob content.

As FileReader inherits from EventTarget, all those events can also be listened for by using the addEventListener method.

Methods

FileReader.abort(): Aborts the read operation. Upon return, the readyState will be DONE.
FileReader.readAsArrayBuffer(): Starts reading the contents of the specified Blob, once finished, the result attribute contains an ArrayBuffer representing the file's data.
FileReader.readAsBinaryString(): Starts reading the contents of the specified Blob, once finished, the result attribute contains the raw binary data from the file as a string.
FileReader.readAsDataURL(): Starts reading the contents of the specified Blob, once finished, the result attribute contains a data: URL representing the file's data.
FileReader.readAsText(): Starts reading the contents of the specified Blob, once finished, the result attribute contains the contents of the file as a text string.

Specifications

Specification	Status	Comment
File API The definition of 'FileReader' in that specification.	Working Draft	Initial definition

Browser compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	7	Yes	3.6 3.6 Prior to Firefox 4, `Blob` parameters were `File` parameters.	10	11	6
Available in workers	Yes	Yes	46	No	11	No
`abort`	7	Yes	3.6	10	11	6
`error`	7	Yes	3.6 3.6 Prior to Firefox 13, the `error` property returned a `FileError` object. From Firefox 13 to Firefox 58, the `error` property returned a `DOMError` object. From Firefox 58, the `error` property returns a `DOMException` object.	10 10 The `error` property returns a `DOMError` object.	11	6 6 The `error` property returns a `DOMError` object.
`onabort`	7	Yes	3.6	10	11	6
`onerror`	7	Yes	3.6	10	11	6
`onload`	7	Yes	3.6	10	11	6
`onloadend`	7	Yes	3.6	10	11	6
`onprogress`	7	Yes	3.6	10	11	6
`readyState`	7	Yes	3.6	10	11	6
`readAsArrayBuffer`	7	Yes	3.6	10	12	6
`readAsBinaryString`	7	Yes	3.6	10	11	6
`readAsDataURL`	7	Yes	3.6	10	11	6
`readAsText`	7	Yes	3.6	10	11	6
`result`	7	Yes	3.6	10	11	6

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	?	Yes	Yes	32	11	6.1	?
Available in workers	Yes	Yes	Yes	46	11	No	?
`abort`	?	Yes	Yes	32	11	6.1	?
`error`	?	Yes	Yes	32 32 From Firefox 32 to Firefox 58, the `error` property returned a `DOMError` object. From Firefox 58, the `error` property returns a `DOMException` object.	11	6.1 6.1 The `error` property returns a `DOMError` object.	?
`onabort`	?	Yes	Yes	32	11	6.1	?
`onerror`	?	Yes	Yes	32	11	6.1	?
`onload`	?	Yes	Yes	32	11	6.1	?
`onloadend`	?	Yes	Yes	32	11	6.1	?
`onprogress`	?	Yes	Yes	32	11	6.1	?
`readyState`	?	Yes	Yes	32	11	6.1	?
`readAsArrayBuffer`	?	Yes	Yes	32	12	6.1	?
`readAsBinaryString`	?	Yes	Yes	32	11	6.1	?
`readAsDataURL`	?	Yes	Yes	32	11	6.1	?
`readAsText`	?	Yes	Yes	32	11	6.1	?
`result`	?	Yes	Yes	32	11	6.1	?