Factor out IsFixedLengthTypedArray AO

spec.html

@@ -14627,12 +14627,8 @@ <h1>[[PreventExtensions]] ( ): a normal completion containing a Boolean</h1>
           <dd>a TypedArray _O_</dd>
         </dl>
         <emu-alg>
-          1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
-          1. Let _taIsFixedLength_ be *true*.
-          1. If _O_.[[ArrayLength]] is ~auto~, set _taIsFixedLength_ to *false*.
-          1. If IsFixedLengthArrayBuffer(_buffer_) is *false* and IsSharedArrayBuffer(_buffer_) is *false*, set _taIsFixedLength_ to *false*.
           1. NOTE: The extensibility-related invariants specified in <emu-xref href="#sec-invariants-of-the-essential-internal-methods"></emu-xref> do not allow this method to return *true* when _O_ can gain (or lose and then regain) integer index properties, which might occur with resizing of its underlying buffer.
-          1. If _taIsFixedLength_ is *false*, return *false*.
+          1. If IsFixedLengthTypedArray(_O_) is *false*, return *false*.
           1. Return OrdinaryPreventExtensions(_O_).
         </emu-alg>
       </emu-clause>
@@ -41847,6 +41843,22 @@ <h1>
             1. Return ~unused~.
           </emu-alg>
         </emu-clause>
+
+        <emu-clause id="sec-isfixedlengthtypedarray" type="abstract operation">
+          <h1>
+            IsFixedLengthTypedArray (
+              _O_: a TypedArray,
+            ): a Boolean
+          </h1>
+          <dl class="header">
+          </dl>
+          <emu-alg>
+            1. If _O_.[[ArrayLength]] is ~auto~, return *false*.
+            1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
+            1. If IsFixedLengthArrayBuffer(_buffer_) is *false* and IsSharedArrayBuffer(_buffer_) is *false*, return *false*.
+            1. Return *true*.
+          </emu-alg>
+        </emu-clause>
       </emu-clause>
     </emu-clause>