don’t expose domain and range for identity (yet)

src/scales.js

@@ -528,11 +528,11 @@ function exposeScale({scale, type, range, domain, interpolate, interval, transfo
   // The domain and range may be missing for non-position identity scales (e.g.,
   // color), and for position identity scales, only the range is computed
   // internally (by autoScaleRange) and then promoted to the domain here.
-  if (type === "identity") domain = range;
+  if (type === "identity") return {type: "identity", apply: (d) => d, invert: (d) => d};
   const unknown = scale.unknown ? scale.unknown() : undefined;
   return {
     type,
-    ...(domain !== undefined && {domain: slice(domain)}), // defensive copy
+    domain: slice(domain), // defensive copy
     ...(range !== undefined && {range: slice(range)}), // defensive copy
     ...(transform !== undefined && {transform}),
     ...(percent && {percent}), // only exposed if truthy

src/scales/quantitative.js

@@ -261,11 +261,8 @@ function isOrdered(domain, sign) {
 // identity scale because it coerces to number; and we can’t compute the domain
 // (and equivalently range) since we can’t know whether the values are
 // continuous or discrete.
-const identityScale = (d) => d;
-identityScale.invert = identityScale;
-
 export function createScaleIdentity(key) {
-  return {type: "identity", scale: hasNumericRange(registry.get(key)) ? scaleIdentity() : identityScale};
+  return {type: "identity", scale: hasNumericRange(registry.get(key)) ? scaleIdentity() : (d) => d};
 }
 
 export function inferDomain(channels, f = finite) {

test/scales/scales-test.js

@@ -2080,7 +2080,7 @@ it("plot(…).scale(name) reflects the given transform", async () => {
 
 it("plot(…).scale(name) can return an identity scale, ignoring all other options", () => {
   const plot = Plot.dot([1, 2], {x: (d) => d, fill: (d) => d}).plot({x: {type: "identity"}, color: {type: "identity"}});
-  scaleEqual(plot.scale("x"), {domain: [20, 620], range: [20, 620], type: "identity"});
+  scaleEqual(plot.scale("x"), {type: "identity"});
   scaleEqual(plot.scale("color"), {type: "identity"});
 });