var upload = function(files) {
        var formData = new FormData(),
            xhr = new XMLHttpRequest(),
            x = 0;

        for(x = 0; x < files.length; x++) {
            formData.append('file[]', files[x]);
        }
        console.log(x);

        xhr.onload = function() {
            var data = JSON.parse(this.responseText);
            displayUploads(data);
        };

        xhr.open('post', 'upload.php');
        xhr.send(formData);
    };

Uncaught SyntaxError: Unexpected token < in JSON at position 0
at JSON.parse (<anonymous>)
at XMLHttpRequest.xhr.onload (строка 55, там где x = 0)