TypeScriptCheatsheet
diff --git a/‎src/compiler/program.ts‎
Lines changed: 1 addition & 1 deletion b/‎src/compiler/program.ts‎
Lines changed: 1 addition & 1 deletion
diff --git a/‎src/compiler/sys.ts‎
Lines changed: 1 addition & 1 deletion b/‎src/compiler/sys.ts‎
Lines changed: 1 addition & 1 deletion
diff --git a/‎src/compiler/watch.ts‎
Lines changed: 13 additions & 2 deletions b/‎src/compiler/watch.ts‎
Lines changed: 13 additions & 2 deletions
@@ -124,7 +124,7 @@ namespace ts {
                 try {
                     writeFileWorker(fileName, data, writeByteOrderMark);
                 }
-                catch (_) {
+                catch {
                     ensureDirectoriesExist(getDirectoryPath(normalizePath(fileName)));
                     writeFileWorker(fileName, data, writeByteOrderMark);
                 }
 
@@ -547,7 +547,7 @@ namespace ts {
             try {
                 originalWriteFile.call(sys, path, data, writeBom);
             }
-            catch (_) {
+            catch {
                 const directoryPath = getDirectoryPath(normalizeSlashes(path));
                 if (directoryPath && !sys.directoryExists(directoryPath)) {
                     recursiveCreateDirectory(directoryPath, sys);
 
@@ -307,9 +307,20 @@ namespace ts {
         function writeFile(fileName: string, text: string, writeByteOrderMark: boolean, onError: (message: string) => void) {
             try {
                 performance.mark("beforeIOWrite");
-                ensureDirectoriesExist(getDirectoryPath(normalizePath(fileName)));
 
-                host.writeFile!(fileName, text, writeByteOrderMark);
+                // PERF: Checking for directory existence is expensive.
+                // Instead, assume the directory exists and fall back
+                // to creating it if the file write fails.
+                // NOTE: If patchWriteFileEnsuringDirectory has been called,
+                // the file write will do its own directory creation and
+                // the ensureDirectoriesExist call will always be redundant.
+                try {
+                    host.writeFile!(fileName, text, writeByteOrderMark);
+                }
+                catch {
+                    ensureDirectoriesExist(getDirectoryPath(normalizePath(fileName)));
+                    host.writeFile!(fileName, text, writeByteOrderMark);
+                }
 
                 performance.mark("afterIOWrite");
                 performance.measure("I/O Write", "beforeIOWrite", "afterIOWrite");
Original file line number	Diff line number	Diff line change
`@@ -124,7 +124,7 @@ namespace ts {`
`124`	`124`	`try {`
`125`	`125`	`writeFileWorker(fileName, data, writeByteOrderMark);`
`126`	`126`	`}`
`127`		`- catch (_) {`
	`127`	`+ catch {`
`128`	`128`	`ensureDirectoriesExist(getDirectoryPath(normalizePath(fileName)));`
`129`	`129`	`writeFileWorker(fileName, data, writeByteOrderMark);`
`130`	`130`	`}`
Original file line number	Diff line number	Diff line change
`@@ -547,7 +547,7 @@ namespace ts {`
`547`	`547`	`try {`
`548`	`548`	`originalWriteFile.call(sys, path, data, writeBom);`
`549`	`549`	`}`
`550`		`- catch (_) {`
	`550`	`+ catch {`
`551`	`551`	`const directoryPath = getDirectoryPath(normalizeSlashes(path));`
`552`	`552`	`if (directoryPath && !sys.directoryExists(directoryPath)) {`
`553`	`553`	`recursiveCreateDirectory(directoryPath, sys);`