Outline or border for the spline series in highcharts - highcharts

Question

I have created a graph using highcharts which has 6 series. 3 are column series and 3 are spline series.spline series will collide or go within the column chart so having a requirement to add outline to spline series to have better viewing. Trying to add a border color for the spline series but unable to do. But the same is possible in column chart.If anyone have tried this before for spline series kindly help.
plotOptions: {
series: {
borderColor: '#303030'
}
},
this bordercolor is working for column but not in spline series
column chart
http://jsfiddle.net/gh/get/library/pure/highcharts/highcharts/tree/master/samples/highcharts/plotoptions/column-bordercolor/
would like to have border for the below series
http://jsfiddle.net/gh/get/library/pure/highcharts/highcharts/tree/master/samples/highcharts/plotoptions/series-datalabels-box/

Answer 1

There is no such feature in Highcharts to set line border, but all is not lost.
You can achieve the effect you want, by adding new "fake" series basing on every line series, and set a couple of parameters.
Best place (in code) to do that would be the chart.events.load function, so there just find all series with line type:
chart: {
events: {
load() {
var series = this.series.filter(elem => elem.type === 'line')
}
}
}
Then, iterate on all the series found, and create new one so that it would have color: [color_you_want], the same data and marker.symbol, increased lineWidth as well as marker.radius, won't be accessible by mouse and not visible in legend, just like below:
chart: {
events: {
load() {
var series = this.series.filter(elem => elem.type === 'line')
series.forEach(series => {
this.addSeries({
data: series.userOptions.data,
showInLegend: false,
color: '#000',
enableMouseTracking: false,
zIndex: -9999,
marker: {
symbol: series.symbol,
radius: series.options.marker.radius + 1
},
lineWidth: series.options.lineWidth + 2
})
})
}
}
}
Hope, it helps you.
Live example: http://jsfiddle.net/yw2tb4nm/
API Reference:
https://api.highcharts.com/highcharts/chart.events.load
https://api.highcharts.com/highcharts/series.line.marker.symbol
https://api.highcharts.com/highcharts/series.line.marker.radius
https://api.highcharts.com/highcharts/series.line.showInLegend
https://api.highcharts.com/highcharts/series.line.enableMouseTracking