gistfile1.diff

diff --git a/src/completion.mjs b/src/completion.mjs
index 6a89ce4..dffb911 100644
--- a/src/completion.mjs
+++ b/src/completion.mjs
@@ -5,10 +5,10 @@ import {
 import { New as NewValue } from './value.mjs';
 
 // #sec-completion-record-specification-type
-export class Completion {
+class Completion {
   constructor(type, value, target) {
-    if (type instanceof Completion) {
-      return type;
+    if (typeof type !== 'string') {
+      throw new TypeError('Completion type is not a string');
     }
     this.Type = type;
     this.Value = value;
@@ -16,6 +16,20 @@ export class Completion {
   }
 }
 
+function CompletionFunction(...args) {
+  if (new.target !== undefined) {
+    return new Completion(...args);
+  }
+  const completion = args[0];
+  return completion;
+}
+Object.defineProperty(
+  CompletionFunction, 'prototype',
+  Object.getOwnPropertyDescriptor(Completion, 'prototype'),
+);
+
+export { CompletionFunction as Completion };
+
 // #sec-normalcompletion
 export class NormalCompletion {
   constructor(value) {
diff --git a/src/runtime-semantics/ForStatement.mjs b/src/runtime-semantics/ForStatement.mjs
index d69bbc5..5d66882 100644
--- a/src/runtime-semantics/ForStatement.mjs
+++ b/src/runtime-semantics/ForStatement.mjs
@@ -59,7 +59,7 @@ function ForBodyEvaluation(test, increment, stmt, perIterationBindings, labelSet
     }
     const result = Evaluate_Statement(stmt);
     if (LoopContinues(result, labelSet).isFalse()) {
-      return new Completion(UpdateEmpty(result, V));
+      return Completion(UpdateEmpty(result, V));
     }
     if (result.Value !== undefined) {
       V = result.Value;
@@ -107,12 +107,12 @@ export function Evaluate_ForStatement(ForStatement, labelSet = []) {
       const forDcl = Evaluate_Statement(ForStatement.init);
       if (forDcl instanceof AbruptCompletion) {
         surroundingAgent.runningExecutionContext.LexicalEnvironment = oldEnv;
-        return new Completion(forDcl);
+        return Completion(forDcl);
       }
       const perIterationLets = isConst ? [] : boundNames;
       const bodyResult = ForBodyEvaluation(ForStatement.test, ForStatement.update, ForStatement.body, perIterationLets, labelSet);
       surroundingAgent.runningExecutionContext.LexicalEnvironment = oldEnv;
-      return new Completion(bodyResult);
+      return Completion(bodyResult);
     }
     default:
       throw outOfRange('Evaluate_ForStatement', ForStatement);
diff --git a/src/runtime-semantics/IfStatement.mjs b/src/runtime-semantics/IfStatement.mjs
index 93ae74e..e13c7e0 100644
--- a/src/runtime-semantics/IfStatement.mjs
+++ b/src/runtime-semantics/IfStatement.mjs
@@ -33,13 +33,13 @@ export function Evaluate_IfStatement({
     } else {
       stmtCompletion = Evaluate_Statement(AlternateStatement);
     }
-    return new Completion(UpdateEmpty(stmtCompletion, NewValue(undefined)));
+    return Completion(UpdateEmpty(stmtCompletion, NewValue(undefined)));
   } else {
     if (exprValue.isFalse()) {
       return new NormalCompletion(undefined);
     } else {
       const stmtCompletion = Evaluate_Statement(Statement);
-      return new Completion(UpdateEmpty(stmtCompletion, NewValue(undefined)));
+      return Completion(UpdateEmpty(stmtCompletion, NewValue(undefined)));
     }
   }
 }