[hsjs] Better handling of JSON property names

.chronus/changes/witemple-msft-quote-property-name-json-2025-4-7-13-40-10.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-server-js"
+---
+
+Fixed an issue in which differences between model and JSON serialized property names were not correctly detected and property names for JSON serialization were not correctly quoted as necessary.

packages/http-server-js/src/common/serialization/json.ts

@@ -20,7 +20,7 @@ import {
 import { getHeaderFieldOptions, getPathParamOptions, getQueryParamOptions } from "@typespec/http";
 import { JsContext, Module } from "../../ctx.js";
 import { reportDiagnostic } from "../../lib.js";
-import { access, parseCase } from "../../util/case.js";
+import { access, objectLiteralProperty, parseCase } from "../../util/case.js";
 import { differentiateUnion, writeCodeTree } from "../../util/differentiate.js";
 import { UnimplementedError } from "../../util/error.js";
 import { indent } from "../../util/iter.js";
@@ -106,10 +106,12 @@ function propertyRequiresJsonSerialization(
   module: Module,
   property: ModelProperty,
 ): boolean {
+  const encodedName = resolveEncodedName(ctx.program, property, "application/json");
+  const jsPropertyName = keywordSafe(parseCase(property.name).camelCase);
   return !!(
     isHttpMetadata(ctx, property) ||
     getEncode(ctx.program, property) ||
-    resolveEncodedName(ctx.program, property, "application/json") !== property.name ||
+    encodedName !== jsPropertyName ||
     (isJsonSerializable(property.type) &&
       requiresJsonSerialization(ctx, module, property.type, property))
   );
@@ -190,7 +192,7 @@ function* emitToJson(
           expr = transposeExpressionToJson(ctx, property.type, expr, module);
         }
 
-        yield `  ${encodedName}: ${expr},`;
+        yield `  ${objectLiteralProperty(encodedName)}: ${expr},`;
       }
 
       yield `};`;

packages/http-server-js/src/util/case.ts

@@ -1,6 +1,8 @@
 // Copyright (c) Microsoft Corporation
 // Licensed under the MIT license.
 
+import { KEYWORDS } from "./keywords.js";
+
 /**
  * Separators recognized by the case parser.
  */
@@ -30,6 +32,17 @@ export function isUnspeakable(name: string): boolean {
 
 const JS_IDENTIFIER = /^[a-zA-Z_$][a-zA-Z0-9_$]*$/;
 
+/**
+ * Returns the property name to be used in an object literal.
+ */
+export function objectLiteralProperty(name: string): string {
+  if (!JS_IDENTIFIER.test(name) || KEYWORDS.has(name)) {
+    return JSON.stringify(name);
+  } else {
+    return name;
+  }
+}
+
 /**
  * Returns an access expression for a given subject and key.
  *