diff --git a/scripts/processDiagnosticMessages.ts b/scripts/processDiagnosticMessages.ts
index 431cf460180..e5eaa46c8e5 100644
--- a/scripts/processDiagnosticMessages.ts
+++ b/scripts/processDiagnosticMessages.ts
@@ -86,7 +86,7 @@ function buildInfoFileOutput(messageTable: InputDiagnosticMessageTable, nameMap:
         '/// <reference path="types.ts" />\r\n' +
         '/* @internal */\r\n' +
         'namespace ts {\r\n' +
-        '    export var Diagnostics = {\r\n';
+        '    export const Diagnostics = {\r\n';
     var names = Utilities.getObjectKeys(messageTable);
     for (var i = 0; i < names.length; i++) {
         var name = names[i];
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 4e1f4553642..e63bcbf8474 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -212,7 +212,7 @@ namespace ts {
      * true for all elements, otherwise returns a new array instance containing the filtered subset.
      */
     export function filter<T, U extends T>(array: T[], f: (x: T) => x is U): U[];
-    export function filter<T>(array: T[], f: (x: T) => boolean): T[]
+    export function filter<T>(array: T[], f: (x: T) => boolean): T[];
     export function filter<T>(array: T[], f: (x: T) => boolean): T[] {
         if (array) {
             const len = array.length;
@@ -1867,10 +1867,10 @@ namespace ts {
         declare var process: any;
         declare var require: any;
 
-        let currentAssertionLevel: AssertionLevel;
+        export let currentAssertionLevel = AssertionLevel.None;
 
         export function shouldAssert(level: AssertionLevel): boolean {
-            return getCurrentAssertionLevel() >= level;
+            return currentAssertionLevel >= level;
         }
 
         export function assert(expression: boolean, message?: string, verboseDebugInfo?: () => string): void {
@@ -1887,35 +1887,6 @@ namespace ts {
         export function fail(message?: string): void {
             Debug.assert(/*expression*/ false, message);
         }
-
-        function getCurrentAssertionLevel() {
-            if (currentAssertionLevel !== undefined) {
-                return currentAssertionLevel;
-            }
-
-            if (sys === undefined) {
-                return AssertionLevel.None;
-            }
-
-            const developmentMode = /^development$/i.test(getEnvironmentVariable("NODE_ENV"));
-            currentAssertionLevel = developmentMode
-                ? AssertionLevel.Normal
-                : AssertionLevel.None;
-
-            return currentAssertionLevel;
-        }
-    }
-
-    export function getEnvironmentVariable(name: string, host?: CompilerHost) {
-        if (host && host.getEnvironmentVariable) {
-            return host.getEnvironmentVariable(name);
-        }
-
-        if (sys && sys.getEnvironmentVariable) {
-            return sys.getEnvironmentVariable(name);
-        }
-
-        return "";
     }
 
     /** Remove an item from an array, moving everything to its right one space left. */
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 91adb09c402..5d46038b2b1 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -206,7 +206,7 @@ namespace ts {
             readFile: fileName => sys.readFile(fileName),
             trace: (s: string) => sys.write(s + newLine),
             directoryExists: directoryName => sys.directoryExists(directoryName),
-            getEnvironmentVariable: name => getEnvironmentVariable(name, /*host*/ undefined),
+            getEnvironmentVariable: name => sys.getEnvironmentVariable ? sys.getEnvironmentVariable(name) : "",
             getDirectories: (path: string) => sys.getDirectories(path),
             realpath
         };
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 2d4fcd241aa..7cf7d75bc02 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -83,7 +83,7 @@ namespace ts {
         getEnvironmentVariable?(name: string): string;
     };
 
-    export var sys: System = (function() {
+    export let sys: System = (function() {
 
         function getWScriptSystem(): System {
 
@@ -637,4 +637,10 @@ namespace ts {
         }
         return sys;
     })();
+
+    if (sys && sys.getEnvironmentVariable) {
+        Debug.currentAssertionLevel = /^development$/i.test(sys.getEnvironmentVariable("NODE_ENV"))
+            ? AssertionLevel.Normal
+            : AssertionLevel.None;
+    }
 }
diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index c6b6b460fca..7c82aeece78 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -509,7 +509,7 @@ namespace Harness {
         tryEnableSourceMapsForHost?(): void;
         getEnvironmentVariable?(name: string): string;
     }
-    export var IO: IO;
+    export let IO: IO;
 
     // harness always uses one kind of new line
     const harnessNewLine = "\r\n";
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index 2b28e66bf88..51310c90a6b 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -12,7 +12,7 @@ namespace ts.server {
     export const maxProgramSizeForNonTsFiles = 20 * 1024 * 1024;
 
     export type ProjectServiceEvent =
-        { eventName: "context", data: { project: Project, fileName: NormalizedPath } } | { eventName: "configFileDiag", data: { triggerFile?: string, configFileName: string, diagnostics: Diagnostic[] } }
+        { eventName: "context", data: { project: Project, fileName: NormalizedPath } } | { eventName: "configFileDiag", data: { triggerFile?: string, configFileName: string, diagnostics: Diagnostic[] } };
 
     export interface ProjectServiceEventHandler {
         (event: ProjectServiceEvent): void;