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I want to convert a html input file to a json string like this:

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

Now, in my firebug:

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.

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migrated from programmers.stackexchange.com Jun 10 at 10:54

This question came from our site for professional programmers interested in conceptual questions about software development.
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1 Answer

up vote 0 down vote

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 );
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Thank you for your answer. I want to send the pointer to another server. So I have to convert the file-pointer to a string. Do you have an idea? –  peacemaker Jun 10 at 13:44
    
Did you read the article ? evt.target.result is a string containing the file content. Using the FileReader API is the only way to fetch it, for security reasons. –  Maël Nison Jun 11 at 14:08
    
I think this is not the solution in my project. There is a problem because I will send the string with GET. The size of the string is too long if the file is for example 500 MB. –  peacemaker Jun 12 at 7:44
    
Well, then don't send it using GET? I'm not sure to understand what you want. If you just need to post a file, do it with FormData rather than JSON, since the former can streamline a file upload without requiring to buffer its content in the RAM. –  Maël Nison Jun 13 at 9:12
    
I want to send the file(-pointer) to another server...so I have to use GET... –  peacemaker Jun 13 at 14:08
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