File type validation with Javascript

Question

I have a question regarding to JavaScript validation. I am validaing the whenever my scripts runs, it validates but also the action

Answer 1

In general, you can use javascript some() method for that.

function isImage(icon) {
  const ext = ['.jpg', '.jpeg', '.bmp', '.gif', '.png', '.svg'];
  return ext.some(el => icon.endsWith(el));
}

let fname = "the file name here.ext";
if (!isImage(fname)) {
  alert("File extension not supported!");
}

Answer 2

The return value of the submit handler affects the submission.

onsubmit="return Checkfiles();"

This is basically saying:

form.onsubmit = function () { return Checkfiles(); };

Answer 3

Upload bulk data through excel sheet(.csv)

$("form").submit(function(){
 var val = $(this).val().toLowerCase();
var regex = new RegExp("(.*?)\.(csv)$");
if(!(regex.test(val))) {
$(this).val('');
alert('Only csv file can be uploaded');
return false;
} 

});

Answer 4

You can use the File Api to test for magic number. Maybe take a look at this answer for other ideas about the validation. More reliable than the file extension check.

Answer 5

You need to return CheckFiles()

Answer 6

var fname = "the file name here.ext";
var re = /(\.jpg|\.jpeg|\.bmp|\.gif|\.png)$/i;
if (!re.exec(fname)) {
  alert("File extension not supported!");
}