Use native maps when they're available

Gulpfile.ts

@@ -330,6 +330,7 @@ const builtGeneratedDiagnosticMessagesJSON = path.join(builtLocalDirectory, "dia
 // processDiagnosticMessages script
 gulp.task(processDiagnosticMessagesJs, false, [], () => {
     const settings: tsc.Settings = getCompilerSettings({
+        target: "es5",
         declaration: false,
         removeComments: true,
         noResolve: false,

scripts/processDiagnosticMessages.ts

@@ -27,7 +27,7 @@ function main(): void {
 
     var inputFilePath = sys.args[0].replace(/\\/g, "/");
     var inputStr = sys.readFile(inputFilePath);
-    
+
     var diagnosticMessages: InputDiagnosticMessageTable = JSON.parse(inputStr);
 
     var names = Utilities.getObjectKeys(diagnosticMessages);
@@ -44,7 +44,7 @@ function main(): void {
 function checkForUniqueCodes(messages: string[], diagnosticTable: InputDiagnosticMessageTable) {
     const originalMessageForCode: string[] = [];
     let numConflicts = 0;
-    
+
     for (const currentMessage of messages) {
         const code = diagnosticTable[currentMessage].code;
 
@@ -74,7 +74,7 @@ function buildUniqueNameMap(names: string[]): ts.Map<string> {
     var uniqueNames = NameGenerator.ensureUniqueness(names, /* isCaseSensitive */ false, /* isFixed */ undefined);
 
     for (var i = 0; i < names.length; i++) {
-        nameMap[names[i]] = uniqueNames[i];
+        nameMap.set(names[i], uniqueNames[i]);
     }
 
     return nameMap;
@@ -91,7 +91,7 @@ function buildInfoFileOutput(messageTable: InputDiagnosticMessageTable, nameMap:
     for (var i = 0; i < names.length; i++) {
         var name = names[i];
         var diagnosticDetails = messageTable[name];
-        var propName = convertPropertyName(nameMap[name]);
+        var propName = convertPropertyName(nameMap.get(name));
 
         result +=
         '        ' + propName +
@@ -114,7 +114,7 @@ function buildDiagnosticMessageOutput(messageTable: InputDiagnosticMessageTable,
     for (var i = 0; i < names.length; i++) {
         var name = names[i];
         var diagnosticDetails = messageTable[name];
-        var propName = convertPropertyName(nameMap[name]);
+        var propName = convertPropertyName(nameMap.get(name));
 
         result += '\r\n  "' + createKey(propName, diagnosticDetails.code) + '"' + ' : "' + name.replace(/[\"]/g, '\\"') + '"';
         if (i !== names.length - 1) {

src/compiler/binder.ts

@@ -349,17 +349,20 @@ namespace ts {
                 // Otherwise, we'll be merging into a compatible existing symbol (for example when
                 // you have multiple 'vars' with the same name in the same container).  In this case
                 // just add this node into the declarations list of the symbol.
-                symbol = symbolTable[name] || (symbolTable[name] = createSymbol(SymbolFlags.None, name));
+                symbol = symbolTable.get(name);
+                if (!symbol) {
+                    symbolTable.set(name, symbol = createSymbol(SymbolFlags.None, name));
+                }
 
                 if (name && (includes & SymbolFlags.Classifiable)) {
-                    classifiableNames[name] = name;
+                    classifiableNames.set(name, name);
                 }
 
                 if (symbol.flags & excludes) {
                     if (symbol.isReplaceableByMethod) {
                         // Javascript constructor-declared symbols can be discarded in favor of
                         // prototype symbols like methods.
-                        symbol = symbolTable[name] = createSymbol(SymbolFlags.None, name);
+                        symbolTable.set(name, symbol = createSymbol(SymbolFlags.None, name));
                     }
                     else {
                         if (node.name) {
@@ -1570,7 +1573,7 @@ namespace ts {
             const typeLiteralSymbol = createSymbol(SymbolFlags.TypeLiteral, "__type");
             addDeclarationToSymbol(typeLiteralSymbol, node, SymbolFlags.TypeLiteral);
             typeLiteralSymbol.members = createMap<Symbol>();
-            typeLiteralSymbol.members[symbol.name] = symbol;
+            typeLiteralSymbol.members.set(symbol.name, symbol);
         }
 
         function bindObjectLiteralExpression(node: ObjectLiteralExpression) {
@@ -1601,9 +1604,9 @@ namespace ts {
                         ? ElementKind.Property
                         : ElementKind.Accessor;
 
-                    const existingKind = seen[identifier.text];
+                    const existingKind = seen.get(identifier.text);
                     if (!existingKind) {
-                        seen[identifier.text] = currentKind;
+                        seen.set(identifier.text, currentKind);
                         continue;
                     }
 
@@ -2208,7 +2211,7 @@ namespace ts {
             constructorFunction.parent = classPrototype;
             classPrototype.parent = leftSideOfAssignment;
 
-            const funcSymbol = container.locals[constructorFunction.text];
+            const funcSymbol = container.locals.get(constructorFunction.text);
             if (!funcSymbol || !(funcSymbol.flags & SymbolFlags.Function || isDeclarationOfFunctionExpression(funcSymbol))) {
                 return;
             }
@@ -2239,7 +2242,7 @@ namespace ts {
                 bindAnonymousDeclaration(node, SymbolFlags.Class, bindingName);
                 // Add name of class expression into the map for semantic classifier
                 if (node.name) {
-                    classifiableNames[node.name.text] = node.name.text;
+                    classifiableNames.set(node.name.text, node.name.text);
                 }
             }
 
@@ -2255,14 +2258,14 @@ namespace ts {
             // module might have an exported variable called 'prototype'.  We can't allow that as
             // that would clash with the built-in 'prototype' for the class.
             const prototypeSymbol = createSymbol(SymbolFlags.Property | SymbolFlags.Prototype, "prototype");
-            if (symbol.exports[prototypeSymbol.name]) {
+            const symbolExport = symbol.exports.get(prototypeSymbol.name);
+            if (symbolExport) {
                 if (node.name) {
                     node.name.parent = node;
                 }
-                file.bindDiagnostics.push(createDiagnosticForNode(symbol.exports[prototypeSymbol.name].declarations[0],
-                    Diagnostics.Duplicate_identifier_0, prototypeSymbol.name));
+                file.bindDiagnostics.push(createDiagnosticForNode(symbolExport.declarations[0], Diagnostics.Duplicate_identifier_0, prototypeSymbol.name));
             }
-            symbol.exports[prototypeSymbol.name] = prototypeSymbol;
+            symbol.exports.set(prototypeSymbol.name, prototypeSymbol);
             prototypeSymbol.parent = symbol;
         }