microsoft · Mar 6, 2018 · Feb 17, 2018 · Feb 17, 2018 · Mar 4, 2018
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -3200,7 +3200,7 @@ namespace ts {
                             }
                         }
 
-                        let entityName: EntityName = undefined;
+                        let entityName: EntityName;
                         const nameIdentifier = symbolToTypeReferenceName(type.symbol);
                         if (qualifiedName) {
                             Debug.assert(!qualifiedName.right);
@@ -5689,7 +5689,7 @@ namespace ts {
                 }
                 return [signature];
             }
-            let result: Signature[] = undefined;
+            let result: Signature[];
             for (let i = 0; i < signatureLists.length; i++) {
                 // Allow matching non-generic signatures to have excess parameters and different return types
                 const match = i === listIndex ? signature : findMatchingSignature(signatureLists[i], signature, /*partialMatch*/ true, /*ignoreThisTypes*/ true, /*ignoreReturnTypes*/ true);
@@ -5707,7 +5707,7 @@ namespace ts {
         // type is the union of the constituent return types.
         function getUnionSignatures(types: Type[], kind: SignatureKind): Signature[] {
             const signatureLists = map(types, t => getSignaturesOfType(t, kind));
-            let result: Signature[] = undefined;
+            let result: Signature[];
             for (let i = 0; i < signatureLists.length; i++) {
                 for (const signature of signatureLists[i]) {
                     // Only process signatures with parameter lists that aren't already in the result list
@@ -5843,7 +5843,7 @@ namespace ts {
             else {
                 // Combinations of function, class, enum and module
                 let members = emptySymbols;
-                let stringIndexInfo: IndexInfo = undefined;
+                let stringIndexInfo: IndexInfo;
                 if (symbol.exports) {
                     members = getExportsOfSymbol(symbol);
                 }
@@ -6395,7 +6395,7 @@ namespace ts {
             }
             const propTypes: Type[] = [];
             const declarations: Declaration[] = [];
-            let commonType: Type = undefined;
+            let commonType: Type;
             for (const prop of props) {
                 if (prop.declarations) {
                     addRange(declarations, prop.declarations);
@@ -6676,7 +6676,7 @@ namespace ts {
                 const parameters: Symbol[] = [];
                 let hasLiteralTypes = false;
                 let minArgumentCount = 0;
-                let thisParameter: Symbol = undefined;
+                let thisParameter: Symbol;
                 let hasThisParameter: boolean;
                 const iife = getImmediatelyInvokedFunctionExpression(declaration);
                 const isJSConstructSignature = isJSDocConstructSignature(declaration);

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
@@ -1590,7 +1590,7 @@ namespace ts {
         return text.replace(/{(\d+)}/g, (_match, index?) => args[+index + baseIndex]);
     }
 
-    export let localizedDiagnosticMessages: MapLike<string> = undefined;
+    export let localizedDiagnosticMessages: MapLike<string>;
 
     export function getLocaleSpecificMessage(message: DiagnosticMessage) {
         return localizedDiagnosticMessages && localizedDiagnosticMessages[message.key] || message.message;
@@ -3049,7 +3049,7 @@ namespace ts {
 
     /** Return the object corresponding to the best pattern to match `candidate`. */
     export function findBestPatternMatch<T>(values: ReadonlyArray<T>, getPattern: (value: T) => Pattern, candidate: string): T | undefined {
-        let matchedValue: T | undefined = undefined;
+        let matchedValue: T | undefined;
         // use length of prefix as betterness criteria
         let longestMatchPrefixLength = -1;
 

diff --git a/src/compiler/moduleNameResolver.ts b/src/compiler/moduleNameResolver.ts
@@ -674,7 +674,7 @@ namespace ts {
         }
 
         // string is for exact match
-        let matchedPattern: Pattern | string | undefined = undefined;
+        let matchedPattern: Pattern | string | undefined;
         if (state.compilerOptions.paths) {
             if (state.traceEnabled) {
                 trace(state.host, Diagnostics.paths_option_is_specified_looking_for_a_pattern_to_match_module_name_0, moduleName);

diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
@@ -4770,7 +4770,7 @@ namespace ts {
             const awaitToken = parseOptionalToken(SyntaxKind.AwaitKeyword);
             parseExpected(SyntaxKind.OpenParenToken);
 
-            let initializer: VariableDeclarationList | Expression = undefined;
+            let initializer: VariableDeclarationList | Expression;
             if (token() !== SyntaxKind.SemicolonToken) {
                 if (token() === SyntaxKind.VarKeyword || token() === SyntaxKind.LetKeyword || token() === SyntaxKind.ConstKeyword) {
                     initializer = parseVariableDeclarationList(/*inForStatementInitializer*/ true);
@@ -6232,7 +6232,7 @@ namespace ts {
                     // Initially we can parse out a tag.  We also have seen a starting asterisk.
                     // This is so that /** * @type */ doesn't parse.
                     let state = JSDocState.SawAsterisk;
-                    let margin: number | undefined = undefined;
+                    let margin: number | undefined;
                     // + 4 for leading '/** '
                     let indent = start - Math.max(content.lastIndexOf("\n", start), 0) + 4;
                     function pushComment(text: string) {
@@ -7256,7 +7256,7 @@ namespace ts {
             }
 
             function getLastChildWorker(node: Node): Node | undefined {
-                let last: Node = undefined;
+                let last: Node;
                 forEachChild(node, child => {
                     if (nodeIsPresent(child)) {
                         last = child;

diff --git a/src/compiler/transformers/utilities.ts b/src/compiler/transformers/utilities.ts
@@ -48,7 +48,7 @@ namespace ts {
         const uniqueExports = createMap<boolean>();
         let exportedNames: Identifier[];
         let hasExportDefault = false;
-        let exportEquals: ExportAssignment = undefined;
+        let exportEquals: ExportAssignment;
         let hasExportStarsToExportValues = false;
         let hasImportStarOrImportDefault = false;
 

diff --git a/src/harness/fourslash.ts b/src/harness/fourslash.ts
@@ -3329,7 +3329,7 @@ ${code}
         const ranges: Range[] = [];
 
         // Stuff related to the subfile we're parsing
-        let currentFileContent: string = undefined;
+        let currentFileContent: string;
         let currentFileName = fileName;
         let currentFileSymlinks: string[] | undefined;
         let currentFileOptions: { [s: string]: string } = {};
@@ -3464,7 +3464,7 @@ ${code}
     }
 
     function recordObjectMarker(fileName: string, location: LocationInformation, text: string, markerMap: ts.Map<Marker>, markers: Marker[]): Marker {
-        let markerValue: any = undefined;
+        let markerValue: any;
         try {
             // Attempt to parse the marker value as JSON
             markerValue = JSON.parse("{ " + text + " }");
@@ -3523,7 +3523,7 @@ ${code}
         let output = "";
 
         /// The current marker (or maybe multi-line comment?) we're parsing, possibly
-        let openMarker: LocationInformation = undefined;
+        let openMarker: LocationInformation;
 
         /// A stack of the open range markers that are still unclosed
         const openRanges: RangeLocationInformation[] = [];

diff --git a/src/harness/harness.ts b/src/harness/harness.ts
@@ -145,7 +145,7 @@ namespace Utils {
             path = "tests/" + path;
         }
 
-        let content: string = undefined;
+        let content: string;
         try {
             content = Harness.IO.readFile(Harness.userSpecifiedRoot + path);
         }
@@ -1891,9 +1891,9 @@ namespace Harness {
             const lines = Utils.splitContentByNewlines(code);
 
             // Stuff related to the subfile we're parsing
-            let currentFileContent: string = undefined;
+            let currentFileContent: string;
             let currentFileOptions: any = {};
-            let currentFileName: any = undefined;
+            let currentFileName: any;
             let refs: string[] = [];
 
             for (const line of lines) {

diff --git a/src/harness/loggedIO.ts b/src/harness/loggedIO.ts
@@ -87,9 +87,9 @@ interface PlaybackControl {
 }
 
 namespace Playback {
-    let recordLog: IoLog = undefined;
-    let replayLog: IoLog = undefined;
-    let replayFilesRead: ts.Map<IoLogFile> | undefined = undefined;
+    let recordLog: IoLog;
+    let replayLog: IoLog;
+    let replayFilesRead: ts.Map<IoLogFile> | undefined;
     let recordLogFileNameBase = "";
 
     interface Memoized<T> {

diff --git a/src/harness/parallel/worker.ts b/src/harness/parallel/worker.ts
@@ -54,8 +54,8 @@ namespace Harness.Parallel.Worker {
         const fakeContext: Mocha.ISuiteCallbackContext = {
             retries() { return this; },
             slow() { return this; },
-            timeout(n) {
-                timeout = n as number;
+            timeout(n: number) {
+                timeout = n;
                 return this;
             },
         };
@@ -126,8 +126,8 @@ namespace Harness.Parallel.Worker {
         let timeout: number;
         const fakeContext: Mocha.ITestCallbackContext = {
             skip() { return this; },
-            timeout(n) {
-                timeout = n as number;
+            timeout(n: number) {
+                timeout = n;
                 const timeoutMsg: ParallelTimeoutChangeMessage = { type: "timeout", payload: { duration: timeout } };
                 process.send(timeoutMsg);
                 return this;

diff --git a/src/harness/projectsRunner.ts b/src/harness/projectsRunner.ts
@@ -163,7 +163,7 @@ class ProjectRunner extends RunnerBase {
             }
 
             function getSourceFile(fileName: string, languageVersion: ts.ScriptTarget): ts.SourceFile {
-                let sourceFile: ts.SourceFile = undefined;
+                let sourceFile: ts.SourceFile;
                 if (fileName === Harness.Compiler.defaultLibFileName) {
                     sourceFile = Harness.Compiler.getDefaultLibrarySourceFile(Harness.Compiler.getDefaultLibFileName(compilerOptions));
                 }
@@ -294,7 +294,7 @@ class ProjectRunner extends RunnerBase {
             }
 
             function getSourceFileText(fileName: string): string {
-                let text: string = undefined;
+                let text: string;
                 try {
                     text = Harness.IO.readFile(getFileNameInTheProjectTest(fileName));
                 }
@@ -370,7 +370,7 @@ class ProjectRunner extends RunnerBase {
                     allInputFiles.unshift({ emittedFileName: sourceFile.fileName, code: sourceFile.text });
                 }
                 else if (!(compilerOptions.outFile || compilerOptions.out)) {
-                    let emitOutputFilePathWithoutExtension: string = undefined;
+                    let emitOutputFilePathWithoutExtension: string;
                     if (compilerOptions.outDir) {
                         let sourceFilePath = ts.getNormalizedAbsolutePath(sourceFile.fileName, compilerResult.program.getCurrentDirectory());
                         sourceFilePath = sourceFilePath.replace(compilerResult.program.getCommonSourceDirectory(), "");

diff --git a/src/server/client.ts b/src/server/client.ts
@@ -607,7 +607,7 @@ namespace ts.server {
             const edits: FileTextChanges[] = this.convertCodeEditsToTextChanges(response.body.edits);
 
             const renameFilename: string | undefined = response.body.renameFilename;
-            let renameLocation: number | undefined = undefined;
+            let renameLocation: number | undefined;
             if (renameFilename !== undefined) {
                 renameLocation = this.lineOffsetToPosition(renameFilename, response.body.renameLocation);
             }

diff --git a/src/server/session.ts b/src/server/session.ts
@@ -1560,7 +1560,7 @@ namespace ts.server {
         }
 
         private extractPositionAndRange(args: protocol.FileLocationOrRangeRequestArgs, scriptInfo: ScriptInfo): { position: number, textRange: TextRange } {
-            let position: number = undefined;
+            let position: number;
             let textRange: TextRange;
             if (this.isLocation(args)) {
                 position = getPosition(args);
@@ -1676,7 +1676,7 @@ namespace ts.server {
         }
 
         private getStartAndEndPosition(args: protocol.FileRangeRequestArgs, scriptInfo: ScriptInfo) {
-            let startPosition: number = undefined, endPosition: number = undefined;
+            let startPosition: number, endPosition: number;
             if (args.startPosition !== undefined) {
                 startPosition = args.startPosition;
             }

diff --git a/src/services/findAllReferences.ts b/src/services/findAllReferences.ts
@@ -509,7 +509,7 @@ namespace ts.FindAllReferences.Core {
             // here appears to be intentional).
             const {
                 text = stripQuotes(unescapeLeadingUnderscores((getLocalSymbolForExportDefault(symbol) || symbol).escapedName)),
-                allSearchSymbols = undefined,
+                allSearchSymbols,
             } = searchOptions;
             const escapedText = escapeLeadingUnderscores(text);
             const parents = this.options.implementations && getParentSymbolsOfPropertyAccess(location, symbol, this.checker);
@@ -1146,7 +1146,7 @@ namespace ts.FindAllReferences.Core {
     }
 
     function getContainingTypeReference(node: Node): Node {
-        let topLevelTypeReference: Node = undefined;
+        let topLevelTypeReference: Node;
 
         while (node) {
             if (isTypeNode(node)) {

diff --git a/src/services/patternMatcher.ts b/src/services/patternMatcher.ts
@@ -336,7 +336,7 @@ namespace ts {
             // Only if all words have some sort of match is the pattern considered matched.
 
             const subWordTextChunks = segment.subWordTextChunks;
-            let matches: PatternMatch[] = undefined;
+            let matches: PatternMatch[];
 
             for (const subWordTextChunk of subWordTextChunks) {
                 // Try to match the candidate with this word
@@ -393,8 +393,8 @@ namespace ts {
 
             let currentCandidate = 0;
             let currentChunkSpan = 0;
-            let firstMatch: number = undefined;
-            let contiguous: boolean = undefined;
+            let firstMatch: number;
+            let contiguous: boolean;
 
             while (true) {
                 // Let's consider our termination cases

diff --git a/src/services/refactors/extractSymbol.ts b/src/services/refactors/extractSymbol.ts
@@ -274,7 +274,7 @@ namespace ts.refactor.extractSymbol {
             }
             else if (isVariableStatement(node)) {
                 let numInitializers = 0;
-                let lastInitializer: Expression | undefined = undefined;
+                let lastInitializer: Expression | undefined;
                 for (const declaration of node.declarationList.declarations) {
                     if (declaration.initializer) {
                         numInitializers++;
@@ -730,12 +730,12 @@ namespace ts.refactor.extractSymbol {
 
         const functionName = createIdentifier(functionNameText);
 
-        let returnType: TypeNode = undefined;
+        let returnType: TypeNode;
         const parameters: ParameterDeclaration[] = [];
         const callArguments: Identifier[] = [];
         let writes: UsageEntry[];
         usagesInScope.forEach((usage, name) => {
-            let typeNode: TypeNode = undefined;
+            let typeNode: TypeNode;
             if (!isJS) {
                 let type = checker.getTypeOfSymbolAtLocation(usage.symbol, usage.node);
                 // Widen the type so we don't emit nonsense annotations like "function fn(x: 3) {"
@@ -1114,7 +1114,7 @@ namespace ts.refactor.extractSymbol {
     }
 
     function getContainingVariableDeclarationIfInList(node: Node, scope: Scope) {
-        let prevNode = undefined;
+        let prevNode;
         while (node !== undefined && node !== scope) {
             if (isVariableDeclaration(node) &&
                 node.initializer === prevNode &&
@@ -1161,7 +1161,7 @@ namespace ts.refactor.extractSymbol {
     }
 
     function getFirstDeclaration(type: Type): Declaration | undefined {
-        let firstDeclaration = undefined;
+        let firstDeclaration;
 
         const symbol = type.symbol;
         if (symbol && symbol.declarations) {
@@ -1297,7 +1297,7 @@ namespace ts.refactor.extractSymbol {
         const members = scope.members;
         Debug.assert(members.length > 0); // There must be at least one child, since we extracted from one.
 
-        let prevMember: ClassElement | undefined = undefined;
+        let prevMember: ClassElement | undefined;
         let allProperties = true;
         for (const member of members) {
             if (member.pos > maxPos) {
@@ -1322,7 +1322,7 @@ namespace ts.refactor.extractSymbol {
     function getNodeToInsertConstantBefore(node: Node, scope: Scope): Statement {
         Debug.assert(!isClassLike(scope));
 
-        let prevScope: Scope | undefined = undefined;
+        let prevScope: Scope | undefined;
         for (let curr = node; curr !== scope; curr = curr.parent) {
             if (isScope(curr)) {
                 prevScope = curr;
@@ -1331,7 +1331,7 @@ namespace ts.refactor.extractSymbol {
 
         for (let curr = (prevScope || node).parent; ; curr = curr.parent) {
             if (isBlockLike(curr)) {
-                let prevStatement = undefined;
+                let prevStatement;
                 for (const statement of curr.statements) {
                     if (statement.pos > node.pos) {
                         break;
@@ -1432,15 +1432,15 @@ namespace ts.refactor.extractSymbol {
         const visibleDeclarationsInExtractedRange: NamedDeclaration[] = [];
         const exposedVariableSymbolSet = createMap<true>(); // Key is symbol ID
         const exposedVariableDeclarations: VariableDeclaration[] = [];
-        let firstExposedNonVariableDeclaration: NamedDeclaration | undefined = undefined;
+        let firstExposedNonVariableDeclaration: NamedDeclaration | undefined;
 
         const expression = !isReadonlyArray(targetRange.range)
             ? targetRange.range
             : targetRange.range.length === 1 && isExpressionStatement(targetRange.range[0])
                 ? (targetRange.range[0] as ExpressionStatement).expression
                 : undefined;
 
-        let expressionDiagnostic: Diagnostic | undefined = undefined;
+        let expressionDiagnostic: Diagnostic | undefined;
         if (expression === undefined) {
             const statements = targetRange.range as ReadonlyArray<Statement>;
             const start = first(statements).getStart();
@@ -1542,7 +1542,7 @@ namespace ts.refactor.extractSymbol {
             }
 
             let hasWrite = false;
-            let readonlyClassPropertyWrite: Declaration | undefined = undefined;
+            let readonlyClassPropertyWrite: Declaration | undefined;
             usagesPerScope[i].usages.forEach(value => {
                 if (value.usage === Usage.Write) {
                     hasWrite = true;

diff --git a/src/services/services.ts b/src/services/services.ts
@@ -1971,7 +1971,7 @@ namespace ts {
                         continue;
                     }
 
-                    let descriptor: TodoCommentDescriptor = undefined;
+                    let descriptor: TodoCommentDescriptor;
                     for (let i = 0; i < descriptors.length; i++) {
                         if (matchArray[i + firstDescriptorCaptureIndex]) {
                             descriptor = descriptors[i];