How to javascript validate <input type=file multiple> if browser does not support multiple [duplicate]

Question

I'm using:

<input type='file' name='pac1[]' multiple>

How do I javascript validate that there is at least one file selected?

When using:

<input type='file' name='pac1'>

I have no problem validating a single non-array entry.

Answer 1

You can use:

<input id="upload" type='file' name='pac1[]' multiple>

And JS:

if(document.getElementById("upload").files.length < 1)
{
   alert("No file selected");
   return false;
}

Answer 2

Bind change event on input type='file' element using addEventListener

INPUTElement.files.length will return number of files selected.

document.querySelector('[name="pac1[]"]').addEventListener('change', function() {
  alert(this.files.length);
});

<input type='file' name='pac1[]' multiple>