[KosBeg]

Общем как меня не учи - я делаю так)

function getContent(timestamp) {

  toQueryString = function(data) {
    var query = '',
      i, push = function(key, value) {
        query += encodeURIComponent(key) + '=' + encodeURIComponent(value) + '&';
      },
      key, value;
    for (key in data) {
      if (!Object.hasOwnProperty.call(data, key)) {
        continue;
      }
      value = data[key];
      if ((typeof(data) === "object") && (data instanceof Array)) {
        for (i = 0; i < value.length; i++) {
          push(key, value[i]);
        };
      } else {
        push(key, data[key]);
      };
    };
    return query.replace(/&$/, '').replace(/%20/g, '+');
  };

  var queryString = {
    'timestamp': timestamp
  };

  var result = fetch('server.php', {
    method: 'post',
    headers: {
      "Content-type": "application/x-www-form-urlencoded"
    },
    body: toQueryString(queryString)
  })

  result.then(function(response) {
    return response.json()
  }).then(function(text) {
    document.querySelector('#response').innerHTML = text.data_from_file;
    getContent(text.timestamp);
  })['catch'](function(ex) {
    getContent(timestamp);
  })
}