diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index ecf64392a9a..57bd9860d12 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -546,7 +546,7 @@ namespace ts {
 
         function getLanguageVariant(fileName: string) {
             // .tsx and .jsx files are treated as jsx language variant.
-            return fileExtensionIs(fileName, ".tsx") || fileExtensionIs(fileName, ".jsx") ?  LanguageVariant.JSX  : LanguageVariant.Standard;
+            return fileExtensionIs(fileName, ".tsx") || fileExtensionIs(fileName, ".jsx") || fileExtensionIs(fileName, ".js") ?  LanguageVariant.JSX  : LanguageVariant.Standard;
         }
 
         function initializeState(fileName: string, _sourceText: string, languageVersion: ScriptTarget, isJavaScriptFile: boolean, _syntaxCursor: IncrementalParser.SyntaxCursor) {
diff --git a/tests/baselines/reference/jsFileCompilationTypeAssertions.errors.txt b/tests/baselines/reference/jsFileCompilationTypeAssertions.errors.txt
index e73ee46fb89..662eea4d405 100644
--- a/tests/baselines/reference/jsFileCompilationTypeAssertions.errors.txt
+++ b/tests/baselines/reference/jsFileCompilationTypeAssertions.errors.txt
@@ -1,9 +1,12 @@
 error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
-tests/cases/compiler/a.js(1,10): error TS8016: 'type assertion expressions' can only be used in a .ts file.
+tests/cases/compiler/a.js(1,10): error TS17008: JSX element 'string' has no corresponding closing tag.
+tests/cases/compiler/a.js(1,27): error TS1005: '</' expected.
 
 
 !!! error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
-==== tests/cases/compiler/a.js (1 errors) ====
+==== tests/cases/compiler/a.js (2 errors) ====
     var v = <string>undefined;
              ~~~~~~
-!!! error TS8016: 'type assertion expressions' can only be used in a .ts file.
\ No newline at end of file
+!!! error TS17008: JSX element 'string' has no corresponding closing tag.
+                              
+!!! error TS1005: '</' expected.
\ No newline at end of file
diff --git a/tests/cases/fourslash/getJavaScriptSemanticDiagnostics20.ts b/tests/cases/fourslash/getJavaScriptSemanticDiagnostics20.ts
deleted file mode 100644
index c34f860b5fe..00000000000
--- a/tests/cases/fourslash/getJavaScriptSemanticDiagnostics20.ts
+++ /dev/null
@@ -1,16 +0,0 @@
-/// <reference path="fourslash.ts" />
-
-// @allowJs: true
-// @Filename: a.js
-//// var v = <string>undefined;
-
-verify.getSyntacticDiagnostics(`[]`);
-verify.getSemanticDiagnostics(`[
-  {
-    "message": "'type assertion expressions' can only be used in a .ts file.",
-    "start": 9,
-    "length": 6,
-    "category": "error",
-    "code": 8016
-  }
-]`);
\ No newline at end of file