C3js timeseries can't show continuous line

Question

I want to use c3 to show device information with timeseries. Here is my json data.

  json: [
            {datetime: '2016-01-02 12:00:01.001', wifi: 1},
            {datetime: '2016-01-02 12:00:01.999', wifi: 0},
            {datetime: '2016-01-02 12:00:03.000', GPS: 0},
            {datetime: '2016-01-02 12:00:04.003', wifi: 1},
            {datetime: '2016-01-02 12:00:05.959', GPS: 1},
            {datetime: '2016-01-02 12:00:06.006', wifi: 0},
        ],

I find it can't show continuous line for each wifi / gps. Is it a bug or any method can show continuous line?

The line what I expected

var chart = c3.generate({
    data: {
        xFormat: '%Y-%M-%d %H:%M:%S.%L',
        json: [
            {datetime: '2016-01-02 12:00:01.001', wifi: 1},
            {datetime: '2016-01-02 12:00:01.999', wifi: 0},
            {datetime: '2016-01-02 12:00:03.000', GPS: 0},
            {datetime: '2016-01-02 12:00:04.003', wifi: 1},
            {datetime: '2016-01-02 12:00:05.959', GPS: 1},
            {datetime: '2016-01-02 12:00:06.006', wifi: 0},
        ],
        keys: {
            x: 'datetime',
            value: ['wifi','GPS'],
        },
        types: {
            wifi: 'line',
            GPS:'line',
        },
    },
    axis: {
        x: {
            type: 'timeseries',
                tick: {
                    format: '%Y-%m-%d %H:%M:%S'
            }
        },
    },
    zoom: {
        enabled: true
    },
});

Source Code

Answer 1

I found that it's an old issue and the solution is "connectNull: true".

    var chart = c3.generate({
    data: {
        xFormat: '%Y-%M-%d %H:%M:%S.%L',
        json: [
            {datetime: '2016-01-02 12:00:01.001', wifi: 1},
            {datetime: '2016-01-02 12:00:01.999', wifi: 0},
            {datetime: '2016-01-02 12:00:04.003', wifi: 1},
            {datetime: '2016-01-02 12:00:06.006', wifi: 0},
            {datetime: '2016-01-02 12:00:03.000', GPS: 0},
            {datetime: '2016-01-02 12:00:05.959', GPS: 1},
        ],
        keys: {
            x: 'datetime',
            value: ['wifi','GPS'],
        },
        types: {
            wifi: 'step',
            GPS:'step',
        },
    },
    axis: {
        x: {
            type: 'timeseries',
                tick: {
                    format: '%Y-%m-%d %H:%M:%S'
            }
        },
    },
    zoom: {
        enabled: true
    },
line: {
    connectNull: true
}
});

SourceCode