[PHP] Get list of monday

get_monday.php

<?php

function getMondaysInRange($dateFromString, $dateToString)
{
  $dateFrom = new \DateTime($dateFromString);
  $dateTo = new \DateTime($dateToString);
  $dates = [];

  if ($dateFrom > $dateTo) {
    return $dates;
  }

  if (1 != $dateFrom->format('N')) {
    $dateFrom->modify('next monday');
  }

  while ($dateFrom <= $dateTo) {
    $dates[] = $dateFrom->format('Y-m-d');
    $dateFrom->modify('+1 week');
  }

  return $dates;
}

$dateFromString = '2018-01-01';
$dateToString = '2018-12-31';
var_dump(getMondaysInRange($dateFromString, $dateToString));