Index: node_modules/d3-shape/src/curve/cardinal.js
===================================================================
--- node_modules/d3-shape/src/curve/cardinal.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-shape/src/curve/cardinal.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,61 @@
+export function point(that, x, y) {
+  that._context.bezierCurveTo(
+    that._x1 + that._k * (that._x2 - that._x0),
+    that._y1 + that._k * (that._y2 - that._y0),
+    that._x2 + that._k * (that._x1 - x),
+    that._y2 + that._k * (that._y1 - y),
+    that._x2,
+    that._y2
+  );
+}
+
+export function Cardinal(context, tension) {
+  this._context = context;
+  this._k = (1 - tension) / 6;
+}
+
+Cardinal.prototype = {
+  areaStart: function() {
+    this._line = 0;
+  },
+  areaEnd: function() {
+    this._line = NaN;
+  },
+  lineStart: function() {
+    this._x0 = this._x1 = this._x2 =
+    this._y0 = this._y1 = this._y2 = NaN;
+    this._point = 0;
+  },
+  lineEnd: function() {
+    switch (this._point) {
+      case 2: this._context.lineTo(this._x2, this._y2); break;
+      case 3: point(this, this._x1, this._y1); break;
+    }
+    if (this._line || (this._line !== 0 && this._point === 1)) this._context.closePath();
+    this._line = 1 - this._line;
+  },
+  point: function(x, y) {
+    x = +x, y = +y;
+    switch (this._point) {
+      case 0: this._point = 1; this._line ? this._context.lineTo(x, y) : this._context.moveTo(x, y); break;
+      case 1: this._point = 2; this._x1 = x, this._y1 = y; break;
+      case 2: this._point = 3; // falls through
+      default: point(this, x, y); break;
+    }
+    this._x0 = this._x1, this._x1 = this._x2, this._x2 = x;
+    this._y0 = this._y1, this._y1 = this._y2, this._y2 = y;
+  }
+};
+
+export default (function custom(tension) {
+
+  function cardinal(context) {
+    return new Cardinal(context, tension);
+  }
+
+  cardinal.tension = function(tension) {
+    return custom(+tension);
+  };
+
+  return cardinal;
+})(0);