var res = await httpFetch('/resource');
if (res instanceof Error)
{
  // FetchError
}
else if (!res)
{
  // JSON falsy values
}
else
{
  // success
}

httpFetch('/resource')
  .then(function(res) {
    if (res instanceof Error)
    {
      // FetchError
    }
    else if (!res)
    {
      // JSON falsy values
    }
    else
    {
      // success
    }
  });

httpFetch('/resource', function(ok, res) {
  if (ok && res)
  {
    // success
  }
  else if (!res)
  {
    // JSON falsy values
  }
  else
  {
    // FetchError
  }
});

var oFetch = httpFetch.create({
  notNull: true
});

var res = await oFetch('/resource');
if (res instanceof Error)
{
  // FetchError
}
else
{
  // success
}

oFetch('/resource')
  .then(function(res) {
    if (res instanceof Error)
    {
      // FetchError
    }
    else
    {
      // success
    }
  });

oFetch('resource', function(ok, res) {
  if (ok)
  {
    // success
  }
  else
  {
    // FetchError
  }
});

var pFetch = httpFetch.create({
  promiseReject: true
});

try
{
  var res = await pFetch('/resource');
  if (res)
  {
    // success
  }
  else
  {
    // JSON falsy values
  }
}
catch (err)
{
  // FetchError
}

oFetch('/resource')
  .then(function(res) {
    if (res)
    {
      // success
    }
    else
    {
      // JSON falsy values
    }
  })
  .catch(function(err)
  {
    // FetchError
  });

var pFetch = httpFetch.create({
  notNull: true,
  promiseReject: true
});

try
{
  var res = await pFetch('/resource');// success
}
catch (err)
{
  // FetchError
}

oFetch('/resource')
  .then(function(res) {
    // success
  })
  .catch(function(err)
  {
    // FetchError
  });

if (res instanceof Error)
{
  switch (res.id)
  {
    case 0:
      ///
      // connection problems:
      // - connection timed out
      // - wrong CORS headers
      // - unsuccessful HTTP STATUSes (not in 200-299 range)
      // - readable stream failed
      // - etc
      ///
      console.log(res.message);   // error details
      console.log(res.response);  // request + response data, full house
      break;
    case 1:
      ///
      // something's wrong with the response data:
      // - empty response
      // - incorrect content type
      // - etc
      ///
      break;
    case 2:
      ///
      // security compromised
      ///
      break;
    case 3:
      ///
      // incorrect API usage
      // - wrong syntax used
      // - something's wrong with the request data
      // - internal bug
      ///
      break;
    case 4:
      ///
      // aborted programmatically:
      // - canceled parsing, before the request was made
      // - canceled fetching, before the response arrived
      // - canceled parsing, after the response arrived
      // - stream canceled
      ///
      break;
    case 5:
      ///
      // unclassified
      ///
      break;
  }
}

var a = httpFetch.create();
var b = a.create();

if ((a instanceof httpFetch) &&
    (b instanceof httpFetch))
{
  // true!
}

// CLIENT (JS)
// let's send a plain content without files,
// there is no need in FormData format, so
// it will be automaticly detected as
// x-www-form-urlencoded:
res = httpFetch.form(url, {
  param1: 1,
  param2: 2,
  param3: 3
});

// CLIENT (JS)
// wait for the response and display it:
console.log(await res);// 6

// CLIENT (JS)
// let's send another request with file attached,
// the body will be sent as
// multipart/form-data:
res = await httpFetch.form(url, {
  param1: 1,
  param2: 2,
  param3: 3,
  fileInput: document.querySelector('input[type="file"]')
});
// SERVER's $_FILES will be populated with uploaded file,
// but the response/result will be the same:
console.log(res);// 6

// instead of GET method, you may POST:
res = await httpFetch(url, {});       // EMPTY OBJECT
res = await httpFetch(url, undefined);// EMPTY BODY
res = await httpFetch(url, null);     // JSON NULL
// it may easily expand to
// into list filters:
res = await httpFetch(url, {
  categories: ['one', 'two'],
  flag: true
});
// or item extras:
res = await httpFetch(url, {
  fullDescription: true,
  ownerInfo: true
});
// OTHERWISE,
// parametrized GET will swamp into:
res = await httpFetch(url+'?flags=123&names=one,two&isPulluted=true');

// DO NOT use multiple/mixed notations:
res = await httpFetch(url+'?more=params', params);
res = await httpFetch(url+'/more/params', params);
// DO unified:
res = await httpFetch(url, Object.assign(params, {more: "params"}));

// by default,
// any HTTP status, except 200 is a FetchError:
if (res instanceof Error) {
  console.log(res.status);
}
else {
  console.log(res.status);// 200
}