Escape quoted parameter names the way parse understands

src/cases.spec.ts

@@ -188,6 +188,20 @@ export const STRINGIFY_TESTS: StringifyTestSet[] = [
     ]),
     expected: '/*"0"',
   },
+  {
+    data: new TokenData([
+      { type: "text", value: "/" },
+      { type: "param", name: "a\tb" },
+    ]),
+    expected: '/:"a\tb"',
+  },
+  {
+    data: new TokenData([
+      { type: "text", value: "/" },
+      { type: "param", name: 'a"b\\c' },
+    ]),
+    expected: '/:"a\\"b\\\\c"',
+  },
   {
     data: new TokenData([
       { type: "text", value: "/users" },

src/index.spec.ts

@@ -240,6 +240,11 @@ describe("path-to-regexp", () => {
         const path = stringify(data);
         expect(path).toEqual(expected);
       });
+
+      it("should parse back to the original tokens", () => {
+        const { tokens } = parse(stringify(data));
+        expect(tokens).toEqual(data.tokens);
+      });
     },
   );
 

src/index.ts

@@ -659,11 +659,21 @@ export function stringify(data: TokenData): string {
  * Stringify a parameter name, escaping when it cannot be emitted directly.
  */
 function stringifyName(name: string, next: Token | undefined): string {
-  if (!ID.test(name)) return JSON.stringify(name);
+  if (!ID.test(name)) return quoteName(name);
 
   if (next?.type === "text" && ID_CONTINUE.test(next.value[0])) {
-    return JSON.stringify(name);
+    return quoteName(name);
   }
 
   return name;
 }
+
+/**
+ * Quote a parameter name using the escape rules understood by `parse`,
+ * which only recognizes a backslash as escaping the next character.
+ * `JSON.stringify` would emit escapes such as `\t` or `\uXXXX` that
+ * `parse` reads back as the literal characters `t` or `uXXXX`.
+ */
+function quoteName(name: string): string {
+  return `"${name.replace(/["\\]/g, "\\$&")}"`;
+}