SaNFeeD

let request = '';
let xhr = new XMLHttpRequest();

xhr.open('GET',  'site.com',  true);
xhr.send();

if (xhr.status != 200) {
  alert( xhr.status + ': ' + xhr.statusText );
} else {
  request =  xhr.responseText;
}

window.onload = () => {
  document.querySelector('.some-element').append(request);
}

<button class="some-class" id="button" data-trigger="false" data-text="Открыть меню">Открыть меню</button>
<div style="display:none;" id="menu" class="some-class">Какое-то меню</div>

const button = document.getElementById('button');
const menu = document.getElementById('menu');

button.addEventListener('click', () =>{
    if(button.dataset.trigger == 'false'){
        button.innerText = 'Закртыть';
        menu.style.display = 'block';
        button.dataset.trigger = true;
    }else{
        button.innerText = button.dataset.text;
        menu.style.display = 'none';
        button.dataset.trigger = false;
    }
});