To create a spline with Konva, we can instantiate a Konva.Line() object with tension attribute.
To define the path of the line you should use points property. If you have three points with x and y coordinates you should define points property as: [x1, y1, x2, y2, x3, y3].
Flat array of numbers should work faster and use less memory than array of objects.
For a full list of attributes and methods, check out the Konva.Line documentation.
{% iframe /downloads/code/shapes/Line_-_Spline.html %}
{% include_code Konva Spline Demo shapes/Line_-_Spline.html %}