How to use the marked.getDefaults function in marked

baseUrl: '',
    gfm: true,
    breaks: false,
    pedantic: false,
    sanitize: true,
    smartLists: true,
    silent: false,
    highlight(code: string, lang: string) {
        return '';
    },
    langPrefix: 'lang-',
    smartypants: false,
    renderer: new marked.Renderer(),
};

options = marked.getDefaults();
options = marked.defaults;

function callback(err: string, markdown: string) {
    console.log('Callback called!');
    return markdown;
}

let myOldMarked: typeof marked = marked.options(options);
myOldMarked = marked.setOptions(options);

console.log(marked('1) I am using __markdown__.'));
console.log(marked('2) I am using __markdown__.', options));
console.log(marked('3) I am using __markdown__.', callback));
console.log(marked('4) I am using __markdown__.', options, callback));

console.log(marked.parse('5) I am using __markdown__.'));