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2026-06-25 21:30:32 +00:00
commit 328faf6251
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+/**
+ * @license
+ * Copyright The Closure Library Authors.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+goog.provide('goog.Thenable');
+
+/** @suppress {extraRequire} used in complex type */
+goog.requireType('goog.Promise');  // for the type reference.
+
+
+
+/**
+ * Provides a more strict interface for Thenables in terms of
+ * http://promisesaplus.com for interop with {@see goog.Promise}.
+ *
+ * @interface
+ * @extends {IThenable<TYPE>}
+ * @template TYPE
+ */
+goog.Thenable = function() {};
+
+
+/**
+ * Adds callbacks that will operate on the result of the Thenable, returning a
+ * new child Promise.
+ *
+ * If the Thenable is fulfilled, the `onFulfilled` callback will be
+ * invoked with the fulfillment value as argument, and the child Promise will
+ * be fulfilled with the return value of the callback. If the callback throws
+ * an exception, the child Promise will be rejected with the thrown value
+ * instead.
+ *
+ * If the Thenable is rejected, the `onRejected` callback will be invoked with
+ * the rejection reason as argument. Similar to the fulfilled case, the child
+ * Promise will then be resolved with the return value of the callback, or
+ * rejected with the thrown value if the callback throws an exception.
+ *
+ * @param {?(function(this:THIS, TYPE): VALUE)=} opt_onFulfilled A
+ *     function that will be invoked with the fulfillment value if the Promise
+ *     is fulfilled.
+ * @param {?(function(this:THIS, *): *)=} opt_onRejected A function that will
+ *     be invoked with the rejection reason if the Promise is rejected.
+ * @param {THIS=} opt_context An optional context object that will be the
+ *     execution context for the callbacks. By default, functions are executed
+ *     with the default this.
+ *
+ * @return {RESULT} A new Promise that will receive the result
+ *     of the fulfillment or rejection callback.
+ * @template VALUE
+ * @template THIS
+ *
+ * When a Promise (or thenable) is returned from the fulfilled callback,
+ * the result is the payload of that promise, not the promise itself.
+ *
+ * @template RESULT := type('goog.Promise',
+ *     cond(isUnknown(VALUE), unknown(),
+ *       mapunion(VALUE, (V) =>
+ *         cond(isTemplatized(V) && sub(rawTypeOf(V), 'IThenable'),
+ *           templateTypeOf(V, 0),
+ *           cond(sub(V, 'Thenable'),
+ *              unknown(),
+ *              V)))))
+ *  =:
+ *
+ */
+goog.Thenable.prototype.then = function(
+    opt_onFulfilled, opt_onRejected, opt_context) {};
+
+
+/**
+ * An expando property to indicate that an object implements
+ * `goog.Thenable`.
+ *
+ * {@see addImplementation}.
+ *
+ * @const
+ */
+goog.Thenable.IMPLEMENTED_BY_PROP = '$goog_Thenable';
+
+
+/**
+ * Marks a given class (constructor) as an implementation of Thenable, so
+ * that we can query that fact at runtime. The class must have already
+ * implemented the interface.
+ * Exports a 'then' method on the constructor prototype, so that the objects
+ * also implement the extern {@see goog.Thenable} interface for interop with
+ * other Promise implementations.
+ * @param {function(new:goog.Thenable,...?)} ctor The class constructor. The
+ *     corresponding class must have already implemented the interface.
+ */
+goog.Thenable.addImplementation = function(ctor) {
+  'use strict';
+  if (COMPILED) {
+    ctor.prototype[goog.Thenable.IMPLEMENTED_BY_PROP] = true;
+  } else {
+    // Avoids dictionary access in uncompiled mode.
+    ctor.prototype.$goog_Thenable = true;
+  }
+};
+
+
+/**
+ * @param {?} object
+ * @return {boolean} Whether a given instance implements `goog.Thenable`.
+ *     The class/superclass of the instance must call `addImplementation`.
+ */
+goog.Thenable.isImplementedBy = function(object) {
+  'use strict';
+  if (!object) {
+    return false;
+  }
+  try {
+    if (COMPILED) {
+      return !!object[goog.Thenable.IMPLEMENTED_BY_PROP];
+    }
+    return !!object.$goog_Thenable;
+  } catch (e) {
+    // Property access seems to be forbidden.
+    return false;
+  }
+};