How can I serialize an input File object to JSON?

I want to convert an HTML input file to a JSON string like this:

var jsonString = JSON.stringify(file);
console.log( file );
console.log( jsonString );

Now, in my Firebug it logs as:

File { size=360195, type="image/jpeg", name="xyz.jpg", mehr...} 
Object {}

Why is the jsonString empty?

Background info: I want to send the file-reference with JSONP to another PHP server.

Additional Information: I want to convert only the file-pointer (reference) to a string, to send it via GET.

Solution 1:

It is not possible to directly convert a File object into JSON using JSON.stringify in Chrome, Firefox and Safari.

You can make a work around to convert File object to string using JSON.stringify

Ex:

// get File Object  
var fileObject = getFile();

// reCreate new Object and set File Data into it
var newObject  = {
   'lastModified'     : fileObject.lastModified,
   'lastModifiedDate' : fileObject.lastModifiedDate,
   'name'             : fileObject.name,
   'size'             : fileObject.size,
   'type'             : fileObject.type
};  
 
// then use JSON.stringify on new object
JSON.stringify(newObject);

You can also add the toJSON() behavior to your File object

EX:

// get File Object  
var fileObject = getFile();

// implement toJSON() behavior  
fileObject.toJSON = function() { return {
   'lastModified'     : myFile.lastModified,
   'lastModifiedDate' : myFile.lastModifiedDate,
   'name'             : myFile.name,
   'size'             : myFile.size,
   'type'             : myFile.type 
};}  
 
// then use JSON.stringify on File object
JSON.stringify(fileObject);

Note: send a File Object to server using the POST HTTP method.

Solution 2:

You have to read the file content using the FileReader API. The File object does not contain the file content (it is just a pointer toward the file, which allows you to read it later).

You can check out this HTML5Rocks article to find out more about the usage of this API.

var file = getAFile( );

var success = function ( content ) {
  console.log( JSON.stringify( content ) ); }

var fileReader = new FileReader( );
fileReader.onload = function ( evt ) { success( evt.target.result ) };
fileReader.readAsText( file );