diff --git a/src/compiler/comments.ts b/src/compiler/comments.ts
index c2cf49eeb6a..cd96981c093 100644
--- a/src/compiler/comments.ts
+++ b/src/compiler/comments.ts
@@ -182,9 +182,9 @@ namespace ts {
             }
         }
 
-        function emitTripleSlashLeadingComment(commentPos: number, commentEnd: number, _kind: SyntaxKind, hasTrailingNewLine: boolean, rangePos: number) {
+        function emitTripleSlashLeadingComment(commentPos: number, commentEnd: number, kind: SyntaxKind, hasTrailingNewLine: boolean, rangePos: number) {
             if (isTripleSlashComment(commentPos, commentEnd)) {
-                emitLeadingComment(commentPos, commentEnd, _kind, hasTrailingNewLine, rangePos);
+                emitLeadingComment(commentPos, commentEnd, kind, hasTrailingNewLine, rangePos);
             }
         }
 
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 05efc6db909..2f77b3040b3 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -903,7 +903,7 @@ namespace ts {
             return t => compose(a(t));
         }
         else {
-            return _t => u => u;
+            return _ => u => u;
         }
     }
 
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index bf540f6a0cd..1051c9adca9 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -14,7 +14,7 @@ namespace ts {
     }
 
     const id = (s: SourceFile) => s;
-    const nullTransformers: Transformer[] = [_ctx => id];
+    const nullTransformers: Transformer[] = [_ => id];
 
     // targetSourceFile is when users only want one file in entire project to be emitted. This is used in compileOnSave feature
     export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFile: SourceFile, emitOnlyDtsFiles?: boolean): EmitResult {
diff --git a/src/compiler/moduleNameResolver.ts b/src/compiler/moduleNameResolver.ts
index ba1f8497559..3fa54f127e1 100644
--- a/src/compiler/moduleNameResolver.ts
+++ b/src/compiler/moduleNameResolver.ts
@@ -5,7 +5,7 @@ namespace ts {
 
     /* @internal */
     export function trace(host: ModuleResolutionHost, message: DiagnosticMessage, ...args: any[]): void;
-    export function trace(host: ModuleResolutionHost, _message: DiagnosticMessage): void {
+    export function trace(host: ModuleResolutionHost): void {
         host.trace(formatMessage.apply(undefined, arguments));
     }
 
diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index 5481dc657b8..8cdbf956d42 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -572,10 +572,10 @@ namespace ts {
         // attached to the EOF token.
         let parseErrorBeforeNextFinishedNode = false;
 
-        export function parseSourceFile(fileName: string, _sourceText: string, languageVersion: ScriptTarget, _syntaxCursor: IncrementalParser.SyntaxCursor, setParentNodes?: boolean, scriptKind?: ScriptKind): SourceFile {
+        export function parseSourceFile(fileName: string, sourceText: string, languageVersion: ScriptTarget, syntaxCursor: IncrementalParser.SyntaxCursor, setParentNodes?: boolean, scriptKind?: ScriptKind): SourceFile {
             scriptKind = ensureScriptKind(fileName, scriptKind);
 
-            initializeState(_sourceText, languageVersion, _syntaxCursor, scriptKind);
+            initializeState(sourceText, languageVersion, syntaxCursor, scriptKind);
 
             const result = parseSourceFileWorker(fileName, languageVersion, setParentNodes, scriptKind);
 
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index bb945824b4d..585fb60df32 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -591,7 +591,7 @@ namespace ts {
                 getExecutingFilePath: () => ChakraHost.executingFile,
                 getCurrentDirectory: () => ChakraHost.currentDirectory,
                 getDirectories: ChakraHost.getDirectories,
-                getEnvironmentVariable: ChakraHost.getEnvironmentVariable || ((_name: string) => ""),
+                getEnvironmentVariable: ChakraHost.getEnvironmentVariable || (() => ""),
                 readDirectory: (path: string, extensions?: string[], excludes?: string[], includes?: string[]) => {
                     const pattern = getFileMatcherPatterns(path, excludes, includes, !!ChakraHost.useCaseSensitiveFileNames, ChakraHost.currentDirectory);
                     return ChakraHost.readDirectory(path, extensions, pattern.basePaths, pattern.excludePattern, pattern.includeFilePattern, pattern.includeDirectoryPattern);