Illuminate\Database\Query\Builder::leftJoin PHP Method

    public function leftJoin($table, $first, $operator = null, $second = null)
    {
        return $this->join($table, $first, $operator, $second, 'left');
    }

 /**
  * @param $table
  * @param $key $table.key
  * @param bool $fkey $this->table.key
  * @return $this
  */
 public function leftJoinOn($table, $key, $fkey = false)
 {
     $fkey = $fkey ?: $key;
     $key = starts_with($key, $table . '.') ? $key : $table . '.' . $key;
     $fkey = starts_with($key, $this->table . '.') ? $fkey : $this->table . '.' . $fkey;
     $this->operator = $this->operator->leftJoin($table, $key, '=', $fkey);
     return $this;
 }