How to use XMLHttpRequest.onload in a loop "for" and after use a table of the response?

Question

I want to use XMLHttpRequest to receive a JSON file from an API. Currently I need to make to REST call (XMLHttpRequest). Then, use the both responses to create a chart using chart.js.

My only problem is asynchronous problem, and I don't know how to avoid it.

I read a lot of topics but I didn't find the solution.

I made a Promise as the following link: How do I promisify native XHR?

May you help me please?

The code below is the code in the main function (as you can see the tab[0] will be empty) :

let tab = []; // make empty table to save the two results in
/*Request to the API */
for (let counterGraphic = 0; counterGraphic < 2; counterGraphic++) {
  let action = 'GET';
  let requestURL = 'http://127.0.0.1:5000/' + counterGraphic + '/'; // sample : http://127.0.0.1:5000/0/
  makeRequest(action, requestURL, tab)
    .then(function(datums) {
      console.log(datums);
    })
    .catch(function(err) {
      console.error('Augh, there was an error!', err.statusText);
    });
}
let first_tab = tab[0];
console.log(tab[0]);

The code bellow is the function makeRequest :

function makeRequest(method, url, tab) {
  return new Promise(function(resolve, reject) {
    let xhr = new XMLHttpRequest();
    xhr.open(method, url);
    xhr.responseType = 'json'; //expected format
    xhr.onload = function() {
      if (this.status >= 200 && this.status < 300) {
        let responseRequest = xhr.response; // response to the REST call
        let responseRequestString = JSON.stringify(responseRequest) // put it inside ' ' 
        let javascriptArray = JSON.parse(responseRequestString); // parsing of the array 
        console.log(javascriptArray[0])
        tab.push(javascriptArray);
        resolve(xhr.response);
      } else {
        reject({
          status: this.status,
          statusText: xhr.statusText
        });
      }
    };
    xhr.onerror = function() {
      reject({
        status: this.status,
        statusText: xhr.statusText
      });
    };
    xhr.send();
  });
}