JavaScript validation for invalid file type

Question

I have a scenario wherein user is trying to view an invalid image file (for example an .dll file renamed to JPG extenstion). How do I alert the user using JavaScript that this is an invalid file?

but the file extension .JPG is valid only but the actual content is of type .dll — JB.
– JB., Commented Nov 19, 2009 at 10:46

Quentin · Accepted Answer · 2009-11-19 10:44:48Z

JavaScript, running in the browser in a standard security context, has no way to determine this.

You have to handle this check server side.

Peter Mortensen · Accepted Answer · 2016-11-20 12:46:34Z

1

There is no way doing it using JavaScript.

edited Nov 20, 2016 at 12:46

Peter Mortensen

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answered Nov 19, 2009 at 10:51

Sarfraz

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Comments

Stuart · Accepted Answer · 2016-11-20 12:54:07Z

There is a way of doing it with javascript.

If the browser supports window.FileReader and window.Blob, which most do, then yes, you can.

if ( window.FileReader && window.Blob ) { // get your file from wherever... // tacky check jpg in the mime type if ( yourFile.type.indexOf("jpeg") ) { .... } }

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