Index: node_modules/d3-scale/src/threshold.js
===================================================================
--- node_modules/d3-scale/src/threshold.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-scale/src/threshold.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,39 @@
+import {bisect} from "d3-array";
+import {initRange} from "./init.js";
+
+export default function threshold() {
+  var domain = [0.5],
+      range = [0, 1],
+      unknown,
+      n = 1;
+
+  function scale(x) {
+    return x != null && x <= x ? range[bisect(domain, x, 0, n)] : unknown;
+  }
+
+  scale.domain = function(_) {
+    return arguments.length ? (domain = Array.from(_), n = Math.min(domain.length, range.length - 1), scale) : domain.slice();
+  };
+
+  scale.range = function(_) {
+    return arguments.length ? (range = Array.from(_), n = Math.min(domain.length, range.length - 1), scale) : range.slice();
+  };
+
+  scale.invertExtent = function(y) {
+    var i = range.indexOf(y);
+    return [domain[i - 1], domain[i]];
+  };
+
+  scale.unknown = function(_) {
+    return arguments.length ? (unknown = _, scale) : unknown;
+  };
+
+  scale.copy = function() {
+    return threshold()
+        .domain(domain)
+        .range(range)
+        .unknown(unknown);
+  };
+
+  return initRange.apply(scale, arguments);
+}