perf(router-core): skip JSON parsing for plain search strings

packages/router-core/src/searchParams.ts

@@ -9,6 +9,29 @@ export const defaultStringifySearch = stringifySearchWith(
   JSON.parse,
 )
 
+function canStringBeJsonParsed(value: string) {
+  if (!value) {
+    return false
+  }
+
+  const firstCharCode = value.charCodeAt(0)
+
+  if (firstCharCode <= 32) {
+    return true
+  }
+
+  return (
+    firstCharCode === 34 ||
+    firstCharCode === 45 ||
+    firstCharCode === 91 ||
+    firstCharCode === 123 ||
+    (firstCharCode >= 48 && firstCharCode <= 57) ||
+    value === 'true' ||
+    value === 'false' ||
+    value === 'null'
+  )
+}
+
 /**
  * Build a `parseSearch` function using a provided JSON-like parser.
  *
@@ -30,7 +53,7 @@ export function parseSearchWith(parser: (str: string) => any) {
     // Try to parse any query params that might be json
     for (const key in query) {
       const value = query[key]
-      if (typeof value === 'string') {
+      if (typeof value === 'string' && canStringBeJsonParsed(value)) {
         try {
           query[key] = parser(value)
         } catch (_err) {
@@ -67,7 +90,11 @@ export function stringifySearchWith(
       } catch (_err) {
         // silent
       }
-    } else if (hasParser && typeof val === 'string') {
+    } else if (
+      hasParser &&
+      typeof val === 'string' &&
+      canStringBeJsonParsed(val)
+    ) {
       try {
         // Check if it's a valid parseable string.
         // If it is, then stringify it again.

packages/router-core/tests/searchParams.test.ts

@@ -1,5 +1,10 @@
-import { describe, expect, test } from 'vitest'
-import { defaultParseSearch, defaultStringifySearch } from '../src'
+import { describe, expect, test, vi } from 'vitest'
+import {
+  defaultParseSearch,
+  defaultStringifySearch,
+  parseSearchWith,
+  stringifySearchWith,
+} from '../src'
 
 describe('Search Params serialization and deserialization', () => {
   /*
@@ -98,4 +103,39 @@ describe('Search Params serialization and deserialization', () => {
       '?foo=%222024-11-18T00%3A00%3A00.000Z%22',
     )
   })
+
+  test('skips parser work for obviously non-json strings', () => {
+    const parser = vi.fn(JSON.parse)
+    const parseSearch = parseSearchWith(parser)
+    const stringifySearch = stringifySearchWith(JSON.stringify, parser)
+
+    expect(parseSearch('?plain=value&other=abc123')).toEqual({
+      plain: 'value',
+      other: 'abc123',
+    })
+    expect(stringifySearch({ plain: 'value', other: 'abc123' })).toEqual(
+      '?plain=value&other=abc123',
+    )
+
+    expect(parser).not.toHaveBeenCalled()
+  })
+
+  test('still parses json-like strings', () => {
+    const parser = vi.fn(JSON.parse)
+    const parseSearch = parseSearchWith(parser)
+    const stringifySearch = stringifySearchWith(JSON.stringify, parser)
+
+    expect(
+      parseSearch('?quoted=%22value%22&object=%7B%22ok%22%3Atrue%7D&num=123'),
+    ).toEqual({
+      quoted: 'value',
+      object: { ok: true },
+      num: 123,
+    })
+    expect(
+      stringifySearch({ quoted: '123', object: { ok: true }, num: '42' }),
+    ).toEqual('?quoted=%22123%22&object=%7B%22ok%22%3Atrue%7D&num=%2242%22')
+
+    expect(parser).toHaveBeenCalled()
+  })
 })