Ok here is a quick regular expression to check if a file name only contains alpha numeric characters also we need to allow the period sign.
/^[0-9a-zA-Z\.]*$/
This allows numbers, letters and the period symbol.
The full code,
var filename = fullfilepath.replace(/^.*[\\\/]/, ''); // this is to get only the file name, file upload field gives the full path if (!filename.match(/^[0-9a-zA-Z\.]*$/)) { alert('File name should only containg letters and numbers, please rename image file and upload.'); }