Add blessed Baseline calculation method

packages/compute-baseline/src/baseline/index.test.ts

@@ -4,10 +4,26 @@ import { Temporal } from "@js-temporal/polyfill";
 import * as chai from "chai";
 import chaiJestSnapshot from "chai-jest-snapshot";
 
-import { computeBaseline, keystoneDateToStatus } from "./index.js";
+import { computeBaseline, getStatus, keystoneDateToStatus } from "./index.js";
 
 chai.use(chaiJestSnapshot);
 
+describe("getStatus", function () {
+  before(function () {
+    chaiJestSnapshot.resetSnapshotRegistry();
+  });
+
+  beforeEach(function () {
+    chaiJestSnapshot.configureUsingMochaContext(this);
+  });
+
+  it("returns a status", function () {
+    const result = getStatus("fetch", "api.Response.json");
+    assert.equal(result.baseline, "high");
+    chai.expect(result).to.matchSnapshot();
+  });
+});
+
 describe("computeBaseline", function () {
   before(function () {
     chaiJestSnapshot.resetSnapshotRegistry();

packages/compute-baseline/src/baseline/index.test.ts.snap

@@ -130,3 +130,20 @@ Object {
 }",
 }
 `;
+
+exports[`getStatus returns a status 1`] = `
+Object {
+  "baseline": "high",
+  "baseline_high_date": "2019-09-27",
+  "baseline_low_date": "2017-03-27",
+  "support": Object {
+    "chrome": "42",
+    "chrome_android": "42",
+    "edge": "14",
+    "firefox": "39",
+    "firefox_android": "39",
+    "safari": "10.1",
+    "safari_ios": "10.3",
+  },
+}
+`;

packages/compute-baseline/src/baseline/index.ts

@@ -44,6 +44,32 @@ interface SupportStatus {
   toJSON: () => string;
 }
 
+/**
+ * Calculate a Baseline status for specific browser compat data keys within a
+ * web-features feature. Use this method to calculate fine-grained support
+ * statuses. This is the only method approved to compute Baseline statuses not
+ * otherwise published in the `web-features` package.
+ *
+ * For example, suppose you want to show a Baseline status for a specific method
+ * in a feature, which might've been supported earlier or later than the broader
+ * feature overall. Then you'd call `getStatus('example-feature',
+ * 'api.ExampleManager.doExample')`.
+ */
+export function getStatus(
+  featureId: string,
+  compatKey: string,
+  compat: Compat = defaultCompat,
+) {
+  // TODO: actually check that featureId is a valid feature
+  // TODO: actually check that compatKey is tagged as featureId in BCD _or_ listed in web-features
+  return JSON.parse(
+    computeBaseline(
+      { compatKeys: [compatKey], checkAncestors: true },
+      compat,
+    ).toJSON(),
+  );
+}
+
 /**
  * Given a set of compat keys, compute the aggregate Baseline support ("high",
  * "low" or false, dates, and releases) for those keys.