Merge pull request #5262 from zhengbli/Fix5127CR

Address code review from 5127

Author: zhengbli

src/compiler/core.ts

@@ -739,13 +739,12 @@ namespace ts {
     export function isSupportedSourceFileName(fileName: string) {
         if (!fileName) { return false; }
 
-        let dotIndex = fileName.lastIndexOf(".");
-        if (dotIndex < 0) {
-            return false;
+        for (let extension of supportedExtensions) {
+            if (fileExtensionIs(fileName, extension)) {
+                return true;
+            }
         }
-
-        let extension = fileName.slice(dotIndex, fileName.length);
-        return supportedExtensions.indexOf(extension) >= 0;
+        return false;
     }
 
     const extensionsToRemove = [".d.ts", ".ts", ".js", ".tsx", ".jsx"];
@@ -846,7 +845,7 @@ namespace ts {
     export function copyListRemovingItem<T>(item: T, list: T[]) {
         let copiedList: T[] = [];
         for (var i = 0, len = list.length; i < len; i++) {
-            if (list[i] != item) {
+            if (list[i] !== item) {
                 copiedList.push(list[i]);
             }
         }

src/server/editorServices.ts

@@ -735,7 +735,7 @@ namespace ts.server {
                     if (!(--project.projectService.directoryWatchersRefCount[directory])) {
                         this.log("Close directory watcher for: " + directory);
                         project.projectService.directoryWatchersForTsconfig[directory].close();
-                        project.projectService.directoryWatchersForTsconfig[directory] = undefined;
+                        delete project.projectService.directoryWatchersForTsconfig[directory];
                     }
                 }
                 this.inferredProjects = copyListRemovingItem(project, this.inferredProjects);