Merge pull request #6562 from RyanCavanaugh/jsIsJsx

Treat .js as JSX

Author: RyanCavanaugh

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) {

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.
+!!! error TS17008: JSX element 'string' has no corresponding closing tag.
+                              
+!!! error TS1005: '</' expected.