convert img to binary.js

//convert image binary
function files_to_urls(files, callback) {
    if (files.length > 0) {
        var promises = [].map.call(files, function (file) {
            return new Promise(function (ok, ng) {
                var reader = new FileReader();
                reader.onload = function (ev) {
                    ok(reader.result);
                };
                reader.onabort = function (ev) {
                    ok(null);
                };
                reader.onerror = function (ev) {
                    ng(reader.error);
                };
                reader.readAsDataURL(file);
            });
        });
        Promise.all(promises)
            .then(callback);
    }
}