Add helper to inject signal values into a function

src/connector.js

@@ -14,6 +14,30 @@ import * as registry from "./internal/registry";
 
 const kind = Symbol.for("connector");
 
+/**
+ * Returns a function that calls `fn` with a list of values extracted from the
+ * provided signals returned by `inputsFn`. Arguments passed to the returned
+ * function are transparently passed to `fn`. `inputsFn` is a function that
+ * returns one or many input signals.
+ *
+ * @example
+ *
+ *  let fn = withInputSignals(
+ *    () => signal("foo"),
+ *    (s, arg) => s + arg,
+ *  );
+ *  fn("bar"); // "foobar"
+ */
+export function withInputSignals(inputsFn, fn) {
+  return (...args) => {
+    let inputs = inputsFn(...args);
+    let values = Array.isArray(inputs)
+      ? inputs.map(s => s.value())
+      : inputs.value();
+    return fn(values, ...args);
+  };
+}
+
 /**
  * Connects to the connector identified by `connectorId`. As a result, a signal
  * is returned which can then be used to access a stream of values reactively

src/connector.test.js

@@ -1,10 +1,33 @@
-import { clearConnectors, connect, connector, rawConnector } from "./connector";
+import {
+  clearConnectors,
+  connect,
+  connector,
+  rawConnector,
+  withInputSignals,
+} from "./connector";
 import { signal, signalFn } from "./signal";
 
 global.console.warn = jest.fn();
 
 beforeEach(() => clearConnectors());
 
+describe("withInputSignals", () => {
+  it("injects extracted value from single input signal", () => {
+    let fn = withInputSignals(
+      () => signal("foo"),
+      (s, ...args) => s + args.join(""),
+    );
+    expect(fn("bar")).toBe("foobar");
+  });
+  it("injects extracted values from multiple input signals", () => {
+    let fn = withInputSignals(
+      () => [signal("foo"), signal("bar")],
+      ([s1, s2], ...args) => s1 + s2 + args.join(""),
+    );
+    expect(fn("baz")).toBe("foobarbaz");
+  });
+});
+
 describe("connect", () => {
   it("returns connector signal", () => {
     connector("foo", () => "bar");

src/index.js

@@ -1,2 +1,7 @@
+export {
+  connect,
+  connector,
+  rawConnector,
+  withInputSignals,
+} from "./connector";
 export { signal, signalFn } from "./signal";
-export { connect, connector, rawConnector } from "./connector";