feat(InputBinding): subscribe callback now supports event priority

NEWS.md

@@ -6,6 +6,8 @@
 
 * `textAreaInput()` gains a `autoresize` option, which automatically resizes the text area to fit its content. (#4210)
 
+* The `callback` argument of Shiny.js' `InputBinding.subscribe()` method gains support for a value of `"event"`. This makes it possible for an input binding to use event priority when updating the value (i.e., send immediately and always resend, even if the value hasn't changed). (#4211)
+
 ## Changes
 
 * Shiny no longer suspends input changes when _any_ `<input type="submit">` or `<button type="submit">` is on the page. Instead, it now only suspends when a `submitButton()` is present. If you have reason for creating a submit button from custom HTML, add a CSS class of `shiny-submit-button` to the button. (#4209)

srcts/src/bindings/input/inputBinding.ts

@@ -1,3 +1,4 @@
+import type { EventPriority } from "../../inputPolicies/inputPolicy";
 import type { RatePolicyModes } from "../../inputPolicies/inputRateDecorator";
 import type { BindScope } from "../../shiny/bind";
 
@@ -26,10 +27,16 @@ class InputBinding {
     el; // unused var
   }
 
-  // The callback method takes one argument, whose value is boolean. If true,
-  // allow deferred (debounce or throttle) sending depending on the value of
-  // getRatePolicy. If false, send value immediately. Default behavior is `false`
-  subscribe(el: HTMLElement, callback: (value: boolean) => void): void {
+  // Historically, the callback value could only be boolean. In this case:
+  //   * false: send value immediately (i.e., priority = "immediate")
+  //   * true: send value later (i.e., priority = "deferred")
+  //     * The input rate policy is also consulted on whether to debounce or throttle
+  // In recent versions, the value can also be "event", meaning that the
+  // value should be sent regardless of whether it has changed.
+  subscribe(
+    el: HTMLElement,
+    callback: (value: EventPriority | boolean) => void
+  ): void {
     // empty
     el; // unused var
     callback; // unused var

srcts/src/shiny/bind.ts

@@ -8,6 +8,7 @@ import type {
   InputRateDecorator,
   InputValidateDecorator,
 } from "../inputPolicies";
+import type { InputPolicyOpts } from "../inputPolicies/inputPolicy";
 import { shinyAppBindOutput, shinyAppUnbindOutput } from "./initedMethods";
 import { sendImageSizeFns } from "./sendImageSize";
 
@@ -27,7 +28,7 @@ function valueChangeCallback(
   inputs: InputValidateDecorator,
   binding: InputBinding,
   el: HTMLElement,
-  allowDeferred: boolean
+  priority: InputPolicyOpts["priority"]
 ) {
   let id = binding.getId(el);
 
@@ -37,17 +38,7 @@ function valueChangeCallback(
 
     if (type) id = id + ":" + type;
 
-    const opts: {
-      priority: "deferred" | "immediate";
-      binding: typeof binding;
-      el: typeof el;
-    } = {
-      priority: allowDeferred ? "deferred" : "immediate",
-      binding: binding,
-      el: el,
-    };
-
-    inputs.setInput(id, value, opts);
+    inputs.setInput(id, value, { priority, binding, el });
   }
 }
 
@@ -272,8 +263,21 @@ function bindInputs(
         const thisBinding = binding;
         const thisEl = el;
 
-        return function (allowDeferred: boolean) {
-          valueChangeCallback(inputs, thisBinding, thisEl, allowDeferred);
+        // Historically speaking, this callback has only accepted a boolean value,
+        // but in recent versions it can also accept an input priority.
+        // The `priority` parameter can be:
+        // - A boolean: `true` maps to "deferred", and `false` maps to "immediate".
+        // - A string or other value representing a specific priority mode, which is passed through as-is.
+        // This conversion ensures backward compatibility while supporting new priority modes.
+        return function (priority: InputPolicyOpts["priority"] | boolean) {
+          const normalizedPriority =
+            typeof priority !== "boolean"
+              ? priority
+              : priority
+              ? "deferred"
+              : "immediate";
+
+          valueChangeCallback(inputs, thisBinding, thisEl, normalizedPriority);
         };
       })();
 

srcts/types/src/bindings/input/inputBinding.d.ts

@@ -1,3 +1,4 @@
+import type { EventPriority } from "../../inputPolicies/inputPolicy";
 import type { RatePolicyModes } from "../../inputPolicies/inputRateDecorator";
 import type { BindScope } from "../../shiny/bind";
 declare class InputBinding {
@@ -6,7 +7,7 @@ declare class InputBinding {
     getId(el: HTMLElement): string;
     getType(el: HTMLElement): string | null;
     getValue(el: HTMLElement): any;
-    subscribe(el: HTMLElement, callback: (value: boolean) => void): void;
+    subscribe(el: HTMLElement, callback: (value: EventPriority | boolean) => void): void;
     unsubscribe(el: HTMLElement): void;
     receiveMessage(el: HTMLElement, data: unknown): Promise<void> | void;
     getState(el: HTMLElement): unknown;