File - Web APIs 编辑

The File interface provides information about files and allows JavaScript in a web page to access their content.

File objects are generally retrieved 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.

A File object is a specific kind of a Blob, and can be used in any context that a Blob can. In particular, FileReader, URL.createObjectURL(), createImageBitmap(), and XMLHttpRequest.send() accept both Blobs and Files.

See Using files from web applications for more information and examples.

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Constructor

File()

Returns a newly constructed File.

Instance properties

File.prototype.lastModified Read only

Returns the last modified time of the file, in millisecond since the UNIX epoch (January 1st, 1970 at Midnight).

File.prototype.lastModifiedDate Read only

Returns the last modified Date of the file referenced by the File object.

File.prototype.nameRead only

Returns the name of the file referenced by the File object.

File.prototype.webkitRelativePath Read only

Returns the path the URL of the File is relative to.

File implements Blob, so it also has the following properties available to it:

File.prototype.size Read only

Returns the size of the file in bytes.

File.prototype.type Read only

Returns the MIME type of the file.

Instance methods

The File interface doesn't define any methods, but inherits methods from the Blob interface:

Blob.prototype.slice([start[, end[, contentType]]])

Returns a new Blob object containing the data in the specified range of bytes of the source Blob.

Blob.prototype.stream()

Transforms the File into a ReadableStream that can be used to read the File contents.

Blob.prototype.text()

Transforms the File into a stream and reads it to completion. It returns a promise that resolves with a USVString (text).

Blob.prototype.arrayBuffer()

Transforms the File into a stream and reads it to completion. It returns a promise that resolves with an ArrayBuffer.

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Using files from web applications
• FileReader
• Using the DOM File API in chrome code (for privileged code running in Gecko, such as Firefox add-ons)