diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 9a4f5452eed..55d2447dd2d 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -844,9 +844,9 @@ 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) {
-                copiedList.push(list[i]);
+        for (let e of list) {
+            if (e !== item) {
+                copiedList.push(e);
             }
         }
         return copiedList;
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 0872a2e5ba5..3eeb126c065 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -407,7 +407,7 @@ namespace ts {
                     // (ref: https://github.com/nodejs/node/pull/2649 and https://github.com/Microsoft/TypeScript/issues/4643)
                     return _fs.watch(
                         path,
-                        { persisten: true, recursive: !!recursive },
+                        { persistent: true, recursive: !!recursive },
                         (eventName: string, relativeFileName: string) => {
                             // In watchDirectory we only care about adding and removing files (when event name is
                             // "rename"); changes made within files are handled by corresponding fileWatchers (when
diff --git a/src/compiler/tsc.ts b/src/compiler/tsc.ts
index 9d79d435a04..e51fda074c5 100644
--- a/src/compiler/tsc.ts
+++ b/src/compiler/tsc.ts
@@ -360,7 +360,8 @@ namespace ts {
             let newFileNames = ts.map(parsedCommandLine.fileNames, compilerHost.getCanonicalFileName);
             let canonicalRootFileNames = ts.map(rootFileNames, compilerHost.getCanonicalFileName);
 
-            if (!arrayStructurallyIsEqualTo(newFileNames, canonicalRootFileNames)) {
+            // We check if the project file list has changed. If so, we just throw away the old program and start fresh.
+            if (!arrayIsEqualTo(newFileNames && newFileNames.sort(), canonicalRootFileNames && canonicalRootFileNames.sort())) {
                 setCachedProgram(undefined);
                 startTimerForRecompilation();
             }
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index ccfab49375d..7c1b606dd00 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -82,17 +82,17 @@ namespace ts {
         return node.end - node.pos;
     }
 
-    export function arrayIsEqualTo<T>(arr1: T[], arr2: T[], comparer?: (a: T, b: T) => boolean): boolean {
-        if (!arr1 || !arr2) {
-            return arr1 === arr2;
+    export function arrayIsEqualTo<T>(array1: T[], array2: T[], equaler?: (a: T, b: T) => boolean): boolean {
+        if (!array1 || !array2) {
+            return array1 === array2;
         }
 
-        if (arr1.length !== arr2.length) {
+        if (array1.length !== array2.length) {
             return false;
         }
 
-        for (let i = 0; i < arr1.length; ++i) {
-            let equals = comparer ? comparer(arr1[i], arr2[i]) : arr1[i] === arr2[i];
+        for (let i = 0; i < array1.length; ++i) {
+            let equals = equaler ? equaler(array1[i], array2[i]) : array1[i] === array2[i];
             if (!equals) {
                 return false;
             }
@@ -2414,16 +2414,4 @@ namespace ts {
             }
         }
     }
-
-    export function arrayStructurallyIsEqualTo<T>(array1: Array<T>, array2: Array<T>): boolean {
-        if (!array1 || !array2) {
-            return false;
-        }
-
-        if (array1.length !== array2.length) {
-            return false;
-        }
-
-        return arrayIsEqualTo(array1.sort(), array2.sort());
-    }
 }
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index 09f8a372463..efcca0e37c5 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -576,7 +576,8 @@ namespace ts.server {
             let newRootFiles = projectOptions.files.map((f => this.getCanonicalFileName(f)));
             let currentRootFiles = project.getRootFiles().map((f => this.getCanonicalFileName(f)));
 
-            if (!arrayStructurallyIsEqualTo(currentRootFiles, newRootFiles)) {
+            // We check if the project file list has changed. If so, we update the project.
+            if (!arrayIsEqualTo(currentRootFiles && currentRootFiles.sort(), newRootFiles && newRootFiles.sort())) {
                 // For configured projects, the change is made outside the tsconfig file, and
                 // it is not likely to affect the project for other files opened by the client. We can 
                 // just update the current project.