Minimum number of files to input

Question

When using <input type="file" multiple> is it possible to ask users to input at least n files?
Ex: <input type="file" min=5 multiple>

Answer 1

JavaScript is required. Add an event listener to listen for the change event on the input, and check the number of uploaded files with .files.length.

var uploader = document.querySelector('input');
var error = document.querySelector('p');
uploader.addEventListener("change", function(){
  if(uploader.files.length < 5){
    error.style.display='block';
  }
})

#error{
  display:none;
  color:red;
}

<input type="file" multiple/>
<p id="error">Please upload at least 5 files</p>

Using it in a form to prevent submission if the number of uploaded files is less than 5:

var uploader = document.querySelector('input');
var error = document.querySelector('p');
function validate(){
  if(uploader.files.length < 5){
    error.style.display='block';
    return false;
  }
}

#error{
  display:none;
  color:red;
}

<form action="somewhere.php" onsubmit="return validate()">
<input type="file" multiple/>
<p id="error">Please upload at least 5 files</p>
<button>Submit files</button>
</form>