repl: check valid syntax by using acorn

nodejs · nodejs-github-bot · Aug 27, 2025 · Mar 6, 2023 · Mar 7, 2023 · Mar 7, 2023
commit c20260e799507ea763ccc4dbc86c6a499972dec4
diff --git a/lib/internal/repl/utils.js b/lib/internal/repl/utils.js
@@ -303,7 +303,7 @@ function setupPreview(repl, contextSymbol, bufferSymbol, active) {
     // curly brace with parenthesis.
     if (StringPrototypeStartsWith(input, '{') &&
       !StringPrototypeEndsWith(input, ';') &&
-      isValidParentheses(input) &&
+      isValidSyntax(input) &&
       !wrapped) {
       input = `(${input})`;
       wrapped = true;
@@ -789,18 +789,24 @@ function isValidParentheses(input) {
         return false;
       }
     }
-  }
-
-  return stack.length === 0;
-}
+    function isValidSyntax(input) {
+      const Parser = require('internal/deps/acorn/acorn/dist/acorn').Parser;
+      try {
+        let result = Parser.parse(input, { ecmaVersion: 'latest' });
+        return true;
+      } catch (e) {
+        return false;
+      }
+    }
 
-module.exports = {
-  REPL_MODE_SLOPPY: Symbol('repl-sloppy'),
-  REPL_MODE_STRICT,
-  isRecoverableError,
-  kStandaloneREPL: Symbol('kStandaloneREPL'),
-  setupPreview,
-  setupReverseSearch,
-  isObjectLiteral,
-  isValidParentheses,
-};
+    module.exports = {
+      REPL_MODE_SLOPPY: Symbol('repl-sloppy'),
+      REPL_MODE_STRICT,
+      isRecoverableError,
+      kStandaloneREPL: Symbol('kStandaloneREPL'),
+      setupPreview,
+      setupReverseSearch,
+      isObjectLiteral,
+      isValidParentheses,
+      isValidSyntax,
+    };
diff --git a/lib/repl.js b/lib/repl.js
@@ -178,6 +178,7 @@ const {
   setupReverseSearch,
   isObjectLiteral,
   isValidParentheses,
+  isValidSyntax,
 } = require('internal/repl/utils');
 const {
   constants: {
@@ -446,8 +447,14 @@ function REPLServer(prompt,
     let awaitPromise = false;
     const input = code;
 
-    if (isObjectLiteral(code)) {
-      // Add parentheses to make sure `code` is parsed as an expression
+    // It's confusing for `{ a : 1 }` to be interpreted as a block
+    // statement rather than an object literal.  So, we first try
+    // to wrap it in parentheses, so that it will be interpreted as
+    // an expression.  Note that if the above condition changes,
+    // lib/internal/repl/utils.js needs to be changed to match.
+    if (RegExpPrototypeExec(/^\s*{/, code) !== null &&
+      RegExpPrototypeExec(/;\s*$/, code) === null &&
+      isValidSyntax(code)) {
       code = `(${StringPrototypeTrim(code)})\n`;
       wrappedCmd = true;
     }
@@ -2157,6 +2164,7 @@ module.exports = {
   REPL_MODE_SLOPPY,
   REPL_MODE_STRICT,
   Recoverable,
+  isValidSyntax,
 };
 
 ObjectDefineProperty(module.exports, 'builtinModules', {