improve error when given invalid scale definition; #772

Author: mbostock

src/scales.js

@@ -1,5 +1,5 @@
 import {parse as isoParse} from "isoformat";
-import {isColor, isEvery, isOrdinal, isFirst, isSymbol, isTemporal, maybeSymbol, order, isTemporalString, isNumericString} from "./options.js";
+import {isColor, isEvery, isOrdinal, isFirst, isSymbol, isTemporal, maybeSymbol, order, isTemporalString, isNumericString, isScaleOptions} from "./options.js";
 import {registry, color, position, radius, opacity, symbol, length} from "./scales/index.js";
 import {ScaleLinear, ScaleSqrt, ScalePow, ScaleLog, ScaleSymlog, ScaleQuantile, ScaleThreshold, ScaleIdentity} from "./scales/quantitative.js";
 import {ScaleDiverging, ScaleDivergingSqrt, ScaleDivergingPow, ScaleDivergingLog, ScaleDivergingSymlog} from "./scales/diverging.js";
@@ -384,6 +384,7 @@ export function scale(options = {}) {
   let scale;
   for (const key in options) {
     if (!registry.has(key)) continue; // ignore unknown properties
+    if (!isScaleOptions(options[key])) continue; // e.g., ignore {color: "red"}
     if (scale !== undefined) throw new Error("ambiguous scale definition");
     scale = exposeScale(normalizeScale(key, options[key]));
   }

test/scales/scales-test.js

@@ -14,6 +14,14 @@ it("Plot.scale(description) returns a standalone scale", () => {
   });
 });
 
+it("Plot.scale({}) throws an error", () => {
+  assert.throws(() => Plot.scale({}), /invalid scale definition/);
+});
+
+it("Plot.scale({color: {}}) throws an error", () => {
+  assert.throws(() => Plot.scale({color: {}}), /invalid scale definition/);
+});
+
 it("plot(…).scale(name) returns undefined for an unused scale", () => {
   const plot = Plot.dot([1, 2], {x: d => d, y: d => d}).plot();
   assert.deepStrictEqual(plot.scale("r"), undefined);