highcharter version of the example found at http://www.highcharts.com/demo/spline-irregular-time

vikjafjellet.R

library(highcharter)
library(tidyverse)

# set up the series data (so many list of lists...)

## dates are one of the toughest things to plot
## the key to understanding this is in the function `highcharter::hc_add_series_time_values`
## in it, you will find how highcharter parses dates, using `highcharter::datetime_to_timestamp`
## which accepts as.Date values, converts to as.POSIXct then to numeric * 1000

series = list(
    list(
        name = 'Winter 2012-2013',
        data = list(
            list(x = 1000*as.numeric(ISOdate(1970, 10, 21)), y = 0),
            list(x = 1000*as.numeric(ISOdate(1970, 11, 4)), y = 0.28),
            list(x = 1000*as.numeric(ISOdate(1970, 11, 9)), y = 0.25),
            list(x = 1000*as.numeric(ISOdate(1970, 11, 27)), y = 0.2),
            list(x = 1000*as.numeric(ISOdate(1970, 12, 2)), y = 0.28),
            list(x = 1000*as.numeric(ISOdate(1970, 12, 26)), y = 0.28),
            list(x = 1000*as.numeric(ISOdate(1970, 12, 29)), y = 0.47),
            list(x = 1000*as.numeric(ISOdate(1971, 1, 11)), y = 0.79),
            list(x = 1000*as.numeric(ISOdate(1971, 1, 26)), y = 0.72),
            list(x = 1000*as.numeric(ISOdate(1971, 2, 3)), y = 1.02),
            list(x = 1000*as.numeric(ISOdate(1971, 2, 11)), y = 1.12),
            list(x = 1000*as.numeric(ISOdate(1971, 2, 25)), y = 1.2),
            list(x = 1000*as.numeric(ISOdate(1971, 3, 11)), y = 1.18),
            list(x = 1000*as.numeric(ISOdate(1971, 4, 11)), y = 1.19),
            list(x = 1000*as.numeric(ISOdate(1971, 5, 1)), y = 1.85),
            list(x = 1000*as.numeric(ISOdate(1971, 5, 5)), y = 2.22),
            list(x = 1000*as.numeric(ISOdate(1971, 5, 19)), y = 1.15),
            list(x = 1000*as.numeric(ISOdate(1971, 6, 3)), y = 0)
        )
    ),
    list(
        name = 'Winter 2013-2014',
        data = list(
            list(x = 1000*as.numeric(ISOdate(1970, 10, 29)), y = 0),
            list(x = 1000*as.numeric(ISOdate(1970, 11, 9)), y = 0.4),
            list(x = 1000*as.numeric(ISOdate(1970, 12, 1)), y = 0.25),
            list(x = 1000*as.numeric(ISOdate(1971, 1, 1)), y = 1.66),
            list(x = 1000*as.numeric(ISOdate(1971, 1, 10)), y = 1.8),
            list(x = 1000*as.numeric(ISOdate(1971, 2, 19)), y = 1.76),
            list(x = 1000*as.numeric(ISOdate(1971, 3, 25)), y = 2.62),
            list(x = 1000*as.numeric(ISOdate(1971, 4, 19)), y = 2.41),
            list(x = 1000*as.numeric(ISOdate(1971, 4, 30)), y = 2.05),
            list(x = 1000*as.numeric(ISOdate(1971, 5, 14)), y = 1.7),
            list(x = 1000*as.numeric(ISOdate(1971, 5, 24)), y = 1.1),
            list(x = 1000*as.numeric(ISOdate(1971, 6, 10)), y = 0)
        )
    ),
    list(
        name = 'Winter 2014-2015',
        data = list(
            list(x = 1000*as.numeric(ISOdate(1970, 11, 25)), y = 0),
            list(x = 1000*as.numeric(ISOdate(1970, 12, 6)), y = 0.25),
            list(x = 1000*as.numeric(ISOdate(1970, 12, 20)), y = 1.41),
            list(x = 1000*as.numeric(ISOdate(1970, 12, 25)), y = 1.64),
            list(x = 1000*as.numeric(ISOdate(1971, 1, 4)), y = 1.6),
            list(x = 1000*as.numeric(ISOdate(1971, 1, 17)), y = 2.55),
            list(x = 1000*as.numeric(ISOdate(1971, 1, 24)), y = 2.62),
            list(x = 1000*as.numeric(ISOdate(1971, 2, 4)), y = 2.5),
            list(x = 1000*as.numeric(ISOdate(1971, 2, 14)), y = 2.42),
            list(x = 1000*as.numeric(ISOdate(1971, 3, 6)), y = 2.74),
            list(x = 1000*as.numeric(ISOdate(1971, 3, 14)), y = 2.62),
            list(x = 1000*as.numeric(ISOdate(1971, 3, 24)), y = 2.6),
            list(x = 1000*as.numeric(ISOdate(1971, 4, 2)), y = 2.81),
            list(x = 1000*as.numeric(ISOdate(1971, 4, 12)), y = 2.63),
            list(x = 1000*as.numeric(ISOdate(1971, 4, 28)), y = 2.77),
            list(x = 1000*as.numeric(ISOdate(1971, 5, 5)), y = 2.68),
            list(x = 1000*as.numeric(ISOdate(1971, 5, 10)), y = 2.56),
            list(x = 1000*as.numeric(ISOdate(1971, 5, 15)), y = 2.39),
            list(x = 1000*as.numeric(ISOdate(1971, 5, 20)), y = 2.3),
            list(x = 1000*as.numeric(ISOdate(1971, 6, 5)), y = 2),
            list(x = 1000*as.numeric(ISOdate(1971, 6, 10)), y = 1.85),
            list(x = 1000*as.numeric(ISOdate(1971, 6, 15)), y = 1.49),
            list(x = 1000*as.numeric(ISOdate(1971, 6, 23)), y = 1.08)
        )
    )
)


hc <- highchart() %>%
    hc_add_series_list(series)

hc %>%
    hc_chart(
        type = 'spline'
    ) %>%
    hc_title(
        text = 'Snow depth at Vikjafjellet, Norway'
    ) %>%
    hc_subtitle(
        text = 'Irregular time data in Highcharts JS'
    ) %>%
    hc_xAxis(
        type = 'datetime',
        dateTimeLabelFormats = list(
            month = '%e. %b',
            year = '%b'
        ),
        title = list(
            text = 'Date'
        )
    ) %>%
    hc_yAxis(
        title = list(
            text = 'Snow depth (m)'
        ),
        min = 0
    ) %>%
    hc_tooltip(
        headerFormat = '<b>{series.name}</b><br>',
        pointFormat = '{point.x:%e. %b}: {point.y:.2f} m'
    ) %>%
    hc_plotOptions(
        spline = list(
            marker = list(
                enabled = TRUE
            )
        )
    )