In javascript charts how do you call series [param{}]. Usually you call a parameter with obj.param = but it doesn't work with series due to []

Question

I have

option{
....
....,
series: [
    {
      data: [
        [0, 70],
        [10, 80],
        [20, 80],
        [30, 80],
        [40, 75]
      ],
      type: 'line',
    },
};

I want to change the type parameter.. I would think of option.series.type = 'bar', But it doesn't work..