Handle click to upload and drag to upload

uploadHandler.js

function init(){
    // default behavior is always show copy icon, open file in new window. override that!
    window.addEventListener('dragover', function(e){
        e.stopPropagation();
        e.preventDefault();
        e.dataTransfer.dropEffect = 'none';
    });
    window.addEventListener('drop', function(e){
        e.stopPropagation();
        e.preventDefault();
    });

    var dropZone = document.getElementById('dropzone');
    dropZone.addEventListener('dragover', function(e) {
        e.stopPropagation();
        e.preventDefault();
        e.dataTransfer.dropEffect = 'copy';
    });

    dropZone.addEventListener('drop', function(e) {
        e.stopPropagation();
        e.preventDefault();
        handleUploads(e.dataTransfer.items);
    });

    var clickToUpload = document.getElementById('uploadBtn');
    var uploadInput = document.getElementById('uploadInput');
    clickToUpload.onclick = function() {
        uploadInput.click();
    };
    uploadInput.addEventListener('change', function(e) {
        handleUploads(e.target.files); // the name "files" may be contingent on <input name="files[]">
    }, false);
}

function handleUploads(items){
    for (var idx=0, len=items.length; idx < len; idx++){
        var file = items[idx];
        if (file.constructor === DataTransferItem){
            file = file.webkitGetAsEntry();
            if (file.isFile){
                handleDataTransferItem(file);
            }
            else if (file.isDirectory){
                expandDirectory(file);
            }
        }
        else if (file.constructor === File){
            readFile(file);
        }
    }
}

function expandDirectory(directory){
    var dirReader = directory.createReader();
    dirReader.readEntries(function(results){
        results.forEach(function(subItem){
            if (subItem.isFile){
                handleDataTransferItem(subItem);
            }
            else if (subItem.isDirectory){
                expandDirectory(subItem);
            }
        });
    });
}

function handleDataTransferItem(entry){
    // skip dot files which are in nested folders, zips, etc
    if (entry.name.startsWith('.')){
        return;
    }
    function onFileWrite(file){
        if (file.fullPath === undefined){
            file.fullPath = entry.fullPath;
        }
        readFile(file);
    }
    function onFileWriteError(error){
        console.error('could not write out file entry!', error);
    }
    entry.file( onFileWrite, onFileWriteError);
}

function readFile(file){
    if (file.name.startsWith('.')){
        return;
    }
    if (file.fullPath === undefined){
        file.fullPath = file.name;
    }
    var fileReader = new FileReader();
    fileReader.onload = function(e) {
        parseFile(file, e.target.result);
    };
    fileReader.onerror = function(e){
        console.error('can not read file contents',e);
    };
    fileReader.readAsText(file);
}

function parseFile(file, fileContents){
    // deal with file
}

init();