constructor (parent, chartGroup) {
        super();

        this._renderArea = false;
        this._dotRadius = DEFAULT_DOT_RADIUS;
        this._dataPointRadius = null;
        this._dataPointFillOpacity = DEFAULT_DOT_OPACITY;
        this._dataPointStrokeOpacity = DEFAULT_DOT_OPACITY;
        this._curve = null;
        this._interpolate = null; // d3.curveLinear;  // deprecated in 3.0
        this._tension = null;  // deprecated in 3.0
        this._defined = undefined;
        this._dashStyle = undefined;
        this._xyTipsOn = true;

        this.transitionDuration(500);
        this.transitionDelay(0);
        this._rangeBandPadding(1);

        this.label(d => utils.printSingleValue(d.y0 + d.y), false);

        this.anchor(parent, chartGroup);
    }
Create a Line Chart.
@example
// create a line chart under #chart-container1 element using the default global chart group
var chart1 = new LineChart('#chart-container1');
// create a line chart under #chart-container2 element using chart group A
var chart2 = new LineChart('#chart-container2', 'chartGroupA');
// create a sub-chart under a composite parent chart
var chart3 = new LineChart(compositeChart);
@param {String|node|d3.selection|CompositeChart} parent - Any valid
{@link https://github.com/d3/d3-selection/blob/master/README.md#select d3 single selector}
specifying a dom block element such as a div; or a dom element or d3 selection.  If the line
chart is a sub-chart in a {@link CompositeChart Composite Chart} then pass in the parent
composite chart instance instead.
@param {String} [chartGroup] - The name of the chart group this chart instance should be placed in.
Interaction with a chart will only trigger events and redraws within the chart's group.