const title = document.querySelector(".first_el_to_change");
title.innerHTML = "--- coucou ;) " + myvar_1;

const ajax_button_1 = document.querySelector("#test_ajax_1");
console.log("ajax_button_1: ");
console.log(ajax_button_1);
ajax_button_1.addEventListener('click', () => {
	ajax_post(ajax_button_1, 'get_data');
});