Normative: add constructor extensions (#54)

Author: legendecas

README.md

@@ -157,9 +157,18 @@ logically-connected sync/async code execution.
 class AsyncContext<T> {
   static wrap<R>(callback: (...args: any[]) => R): (...args: any[]) => R;
 
+  constructor(options: AsyncContextOptions<T>);
+
+  get name(): string;
+
   run<R>(value: T, callback: () => R): R;
 
-  get(): T;
+  get(): T | undefined;
+}
+
+interface AsyncContextOptions<T> {
+  name?: string;
+  defaultValue?: T;
 }
 ```
 

spec.html

@@ -372,13 +372,21 @@ <h1>The AsyncContext Constructor</h1>
       </ul>
 
       <emu-clause id="sec-asynccontext">
-        <h1>AsyncContext ( )</h1>
+        <h1>AsyncContext ( _options_ )</h1>
         <p>This function performs the following steps when called:</p>
 
         <emu-alg>
           1. If NewTarget is *undefined*, throw a *TypeError* exception.
+          1. If _options_ is an Object, then
+            1. Let _name_ be ? Get(_options_, *"name"*).
+            1. Let _nameStr_ be ? ToString(_name_).
+            1. Let _defaultValue_ be ? Get(_options_, *"defaultValue"*).
+          1. Else,
+            1. Let _nameStr_ be the empty String.
+            1. Let _defaultValue_ be *undefined*.
           1. Let _asyncContext_ be ? OrdinaryCreateFromConstructor(NewTarget, *"%AsyncContext.prototype%"*, « [[AsyncContextKey]] »).
-          1. Set _asyncContext_.[[AsyncContextKey]] to a new Symbol.
+          1. Set _asyncContext_.[[AsyncContextKey]] to a new Symbol whose [[Description]] is _nameStr_.
+          1. Set _asyncContext_.[[AsyncContextDefaultValue]] to _defaultValue_.
           1. Return _asyncContext_.
         </emu-alg>
       </emu-clause>
@@ -463,11 +471,23 @@ <h1>AsyncContext.prototype.get ( )</h1>
           1. Let _asyncContextMapping_ be _agentRecord_.[[AsyncContextMapping]].
           1. For each Record { [[AsyncContextKey]], [[AsyncContextValue]] } _p_ of _asyncContextMapping_, do
             1. If SameValueZero(_p_.[[AsyncContextKey]], _asyncContext_.[[AsyncContextKey]]) is *true*, return _p_.[[AsyncContextValue]].
-          1. Return *undefined*.
+          1. Return _asyncContext_.[[AsyncContextDefaultValue]].
         </emu-alg>
       </emu-clause>
     </emu-clause>
 
+    <emu-clause id="sec-asynccontext.prototype.name">
+      <h1>get AsyncContext.prototype.name</h1>
+      <p>`AsyncContext.prototype.name` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps when called:</p>
+      <emu-alg>
+        1. Let _asyncContext_ be the *this* value.
+        1. Perform ? RequireInternalSlot(_asyncContext_, [[AsyncContextKey]]).
+        1. Let _asyncContextKey_ be _asyncContext_.[[AsyncContextKey]].
+        1. Assert: _asyncContextKey_ is a Symbol.
+        1. Return _asyncContextKey_.[[Description]].
+      </emu-alg>
+    </emu-clause>
+
     <emu-clause id="sec-properties-of-asynccontext-instances">
       <h1>Properties of AsyncContext Instances</h1>
       <p>AsyncContext instances are ordinary objects that inherit properties from the AsyncContext prototype object (the intrinsic, %AsyncContext.prototype%). AsyncContext instances are initially created with the internal slots described in <emu-xref href="#table-internal-slots-of-asynccontext-instances"></emu-xref>.</p>
@@ -496,6 +516,17 @@ <h1>Properties of AsyncContext Instances</h1>
               Represents the AsyncContext instance in the surrounding agent's Agent Record's [[AsyncContextMapping]].
             </td>
           </tr>
+          <tr>
+            <td>
+              [[AsyncContextDefaultValue]]
+            </td>
+            <td>
+              an ECMAScript language value
+            </td>
+            <td>
+              The default value of the AsyncContext instance when no entry is found in the mapping.
+            </td>
+          </tr>
         </table>
       </emu-table>
     </emu-clause>