Simplify checking for octal literals in parser

Author: JsonFreeman

src/compiler/parser.ts

@@ -1055,25 +1055,25 @@ module ts {
         function parseLiteralNode(): LiteralExpression {
             var node = <LiteralExpression>createNode(token);
             node.text = scanner.getTokenValue();
+            var tokenPos = scanner.getTokenPos();
             nextToken();
             finishNode(node);
 
             // Octal literals are not allowed in strict mode or ES5
-            if (node.kind === SyntaxKind.NumericLiteral && (isInStrictMode || languageVersion >= ScriptTarget.ES5)) {
-                var numberLiteralSource = getSourceTextOfNodeFromSourceText(sourceText, node);
-                // This regex checks if the number is written in octal
-                // Note that theoretically would match literals like 009, which is not octal. But because
-                // of how the scanner separates the tokens, we would never get a token like this. Instead,
-                // we would get 00 and 9 as two separate tokens.
-                // We also do not need to check for negatives because any prefix operator would be part of a
-                // parent unary expression.
-                if (/0[0-7]+/.test(numberLiteralSource)) {
-                    if (isInStrictMode) {
-                        grammarErrorOnNode(node, Diagnostics.Octal_literals_are_not_allowed_in_strict_mode);
-                    }
-                    else {
-                        grammarErrorOnNode(node, Diagnostics.Octal_literals_are_not_available_when_targeting_ECMAScript_5_and_higher);
-                    }
+            // Note that theoretically the following condition would hold true literals like 009,
+            // which is not octal.But because of how the scanner separates the tokens, we would
+            // never get a token like this.Instead, we would get 00 and 9 as two separate tokens.
+            // We also do not need to check for negatives because any prefix operator would be part of a
+            // parent unary expression.
+            if (node.kind === SyntaxKind.NumericLiteral
+                && sourceText.charCodeAt(tokenPos) === CharacterCodes._0
+                && isOctalDigit(sourceText.charCodeAt(tokenPos + 1))) {
+
+                if (isInStrictMode) {
+                    grammarErrorOnNode(node, Diagnostics.Octal_literals_are_not_allowed_in_strict_mode);
+                }
+                else if (languageVersion >= ScriptTarget.ES5) {
+                    grammarErrorOnNode(node, Diagnostics.Octal_literals_are_not_available_when_targeting_ECMAScript_5_and_higher);
                 }
             }
 

src/compiler/scanner.ts

@@ -300,7 +300,7 @@ module ts {
         return ch >= CharacterCodes._0 && ch <= CharacterCodes._9;
     }
 
-    function isOctalDigit(ch: number): boolean {
+    export function isOctalDigit(ch: number): boolean {
         return ch >= CharacterCodes._0 && ch <= CharacterCodes._7;
     }