Use 'lastOrUndefined' where appropriate in the services layer.

Author: DanielRosenwasser

src/services/breakpoints.ts

@@ -446,14 +446,14 @@ module ts.BreakpointResolver {
                         // fall through.
 
                     case SyntaxKind.CatchClause:
-                        return spanInNode((<Block>node.parent).statements[(<Block>node.parent).statements.length - 1]);;
+                        return spanInNode(lastOrUndefined((<Block>node.parent).statements));;
 
                     case SyntaxKind.CaseBlock:
                         // breakpoint in last statement of the last clause
                         let caseBlock = <CaseBlock>node.parent;
-                        let lastClause = caseBlock.clauses[caseBlock.clauses.length - 1];
+                        let lastClause = lastOrUndefined(caseBlock.clauses);
                         if (lastClause) {
-                            return spanInNode(lastClause.statements[lastClause.statements.length - 1]);
+                            return spanInNode(lastOrUndefined(lastClause.statements));
                         }
                         return undefined;
 

src/services/formatting/formattingScanner.ts

@@ -51,7 +51,7 @@ module ts.formatting {
             if (isStarted) {
                 if (trailingTrivia) {
                     Debug.assert(trailingTrivia.length !== 0);
-                    wasNewLine = trailingTrivia[trailingTrivia.length - 1].kind === SyntaxKind.NewLineTrivia;
+                    wasNewLine = lastOrUndefined(trailingTrivia).kind === SyntaxKind.NewLineTrivia;
                 }
                 else {
                     wasNewLine = false;

src/services/services.ts

@@ -848,7 +848,7 @@ module ts {
                                 // Overwrite the last declaration if it was an overload
                                 // and this one is an implementation.
                                 if (functionDeclaration.body && !(<FunctionLikeDeclaration>lastDeclaration).body) {
-                                    declarations[declarations.length - 1] = functionDeclaration;
+                                    lastOrUndefined(declarations) = functionDeclaration;
                                 }
                             }
                             else {
@@ -4058,7 +4058,7 @@ module ts {
                     return true;
                 }
                 else if (declarations.length) {
-                    result.push(createDefinitionInfo(declarations[declarations.length - 1], symbolKind, symbolName, containerName));
+                    result.push(createDefinitionInfo(lastOrUndefined(declarations), symbolKind, symbolName, containerName));
                     return true;
                 }
 

src/services/utilities.ts

@@ -200,7 +200,7 @@ module ts {
     function nodeEndsWith(n: Node, expectedLastToken: SyntaxKind, sourceFile: SourceFile): boolean {
         let children = n.getChildren(sourceFile);
         if (children.length) {
-            let last = children[children.length - 1];
+            let last = lastOrUndefined(children);
             if (last.kind === expectedLastToken) {
                 return true;
             }