// Assuming <input type="file" id="upload" multiple>

var uploadInput = document.getElementById('upload');

uploadInput.addEventListener('change', function() {
 console.log(uploadInput.files) // File listing!
});

for (var i = 0, fileCount = uploadInput.files.length; i < fileCount; i++) {
 console.log(files[i]);
}

{
 lastModified: 1428005315000,
 lastModifiedDate: Thu Apr 02 2015 15:08:35 GMT-0500 (CDT),
 name: "profile.pdf",
 size: 135568,
 type: "application/pdf",
 webkitRelativePath: ""
}

var maxAllowedSize = 500000;

for (var i = 0, fileCount = uploadInput.files.length, totalSize = 0; i < fileCount; i++) {
 totalSize += files[i].size;
 if(totalSize > maxAllowedSize) {
 // Notify the user that their file(s) are too large
 }

 if(files[i].type != 'application/pdf') {
 // Notify of invalid file type for file in question
 }
}