React Common - Object Structures - FileSystemError

const objectProvider = new DevExpress.fileManagement.ObjectFileSystemProvider({ data: fileSystem });
const keepExtensionsProvider = new DevExpress.fileManagement.CustomFileSystemProvider({
    getItems: function(item) {
        return objectProvider.getItems(item);
    },
    renameItem: function(item, newName) {
        return new Promise((resolve, reject) => {
            if(item.getFileExtension() !== getExtension(newName)) {
                // 1 - reject
                reject(new DevExpress.fileManagement.FileSystemError(5, item, "You cannot change the file extension."));
                // 2 - throw
                // throw new DevExpress.fileManagement.FileSystemError(5, item, "You cannot change the file extension.");
            } else {
                resolve(objectProvider.renameItem(item, newName));
            }
        });
    }
});
const getExtension = function(path) {
    const index = path.lastIndexOf(".");
    return index !== -1 ? path.substr(index) : "";
}
 
$("#file-manager").dxFileManager({ 
    fileSystemProvider: keepExtensionsProvider,
    permissions: { rename: true }
});

var fileSystem = [
    {
        name: "Documents",
        isDirectory: true,
        items: [
            {
                name: "Projects",
                isDirectory: true,
                items: [
                    {
                        name: "About.rtf",
                        isDirectory: false,
                        size: 1024
                    },
                    {
                        name: "Passwords.rtf",
                        isDirectory: false,
                        size: 2048
                    }
                ]
            },
            {
                name: "About.xml",
                isDirectory: false,
                size: 1024
            },
            {
                name: "Managers.rtf",
                isDirectory: false,
                size: 2048
            },
            {
                name: "ToDo.txt",
                isDirectory: false,
                size: 3072
            }
        ],
    },
    {
        name: "Images",
        isDirectory: true,
        items: [
            {
                name: "logo.png",
                isDirectory: false,
                size: 20480
            },
            {
                name: "banner.gif",
                isDirectory: false,
                size: 10240
            }
        ]
    },
    {
        name: "System",
        isDirectory: true,
        items: [
            {
                name: "Employees.txt",
                isDirectory: false,
                size: 3072
            },
            {
                name: "PasswordList.txt",
                isDirectory: false,
                size: 5120
            }
        ]
    },
    {
        name: "Description.rtf",
        isDirectory: false,
        size: 1024
    },
    {
        name: "Description.txt",
        isDirectory: false,
        size: 2048
    }
];