J2CL Read File contents

j2clreadfile.java

        // add to html:
        // <input type="file" id="file-selector" multiple>
        HTMLInputElement fileSelector = (HTMLInputElement) DomGlobal.document.getElementById("file-selector");
        fileSelector.addEventListener("change", event -> {
            FileList files = ((HTMLInputElement) (event.target)).files;
            for (int i = 0; i < files.length; i++) {
                File file = files.item(i);
                file.arrayBuffer()
                    .then(
                        success -> {
                            DomGlobal.alert("success: \n" + success.byteLength);
                            return null;
                        },
                        error -> {
                            DomGlobal.alert("error: " + error);
                            return null;
                        }
                    );
                DomGlobal.alert(file.name);
            }
        });