Wie im Bild gezeigt, können Sie den Wert im erweiterten Zustand sehen, aber der Wert ist nicht tatsächlich im Objekt enthalten

if (typeof require !== 'undefined') var XLSX = require('xlsx');

function to_json(workbook) {
    var result = {};
    workbook.SheetNames.forEach(function(sheetName) {
        var roa = XLSX.utils.sheet_to_row_object_array(workbook.Sheets[sheetName]);
        if (roa.length > 0) {
            result[sheetName] = roa;
        }
    });
    return result;
}
export function handleFile(e) {
    var files = e.target.files;
    var i, f;
    var testTest = {};
    for (i = 0; i != files.length; ++i) {
        f = files[i];
        var reader = new FileReader();
        var name = f.name;
        reader.onload = function(e) {
            var data = e.target.result;
            var workbook;
            /* if binary string, read with type 'binary' */
            workbook = XLSX.read(data, {
                type: 'binary'
            });
            let excelData = to_json(workbook);
            testTest.data = excelData;
        };
        reader.readAsBinaryString(f);
    }
    console.log(testTest)
    return testTest

}