+https://davidwalsh.name/multiple-file-upload

The HTML

<!-- IMPORTANT:  FORM's enctype must be "multipart/form-data" -->
<form method="post" action="upload-page.php" enctype="multipart/form-data">
  <input name="filesToUpload[]" id="filesToUpload" type="file" multiple="" />
</form>

Simply adding the multiple attribute allows for multiple files to be uploaded via one INPUT element.  If you’re a stickler for validation, you’ll want to assign the multiple attribute a value of multiple.

Listing Multiple Files with JavaScript

//get the input and UL list
var input = document.getElementById('filesToUpload');
var list = document.getElementById('fileList');

//empty list for now...
while (list.hasChildNodes()) {
	list.removeChild(ul.firstChild);
}

//for every file...
for (var x = 0; x < input.files.length; x++) {
	//add to list
	var li = document.createElement('li');
	li.innerHTML = 'File ' + (x + 1) + ':  ' + input.files[x].name;
	list.append(li);
}

The input.files property provides an array of files for which you can check the length;  if there’s a length, you can loop through each file and access the file paths and names.

Receiving and Handling Files with PHP

if(count($_FILES['uploads']['filesToUpload'])) {
	foreach ($_FILES['uploads']['filesToUpload'] as $file) {
	    
		//do your upload stuff here
		echo $file;
		
	}
}

PHP creates an array of the files uploaded with the given INPUT’s name.  This variable will always be an array within PHP.