diff --git a/packages/vite/src/node/__tests__/plugins/asset.spec.ts b/packages/vite/src/node/__tests__/plugins/asset.spec.ts
new file mode 100644
index 00000000000000..dcf81c843c6461
--- /dev/null
+++ b/packages/vite/src/node/__tests__/plugins/asset.spec.ts
@@ -0,0 +1,57 @@
+import MagicString from 'magic-string'
+import { describe, expect, test } from 'vitest'
+import { assetUrlRE, writeRuntimeAssetReplacement } from '../../plugins/asset'
+
+describe('writeRuntimeAssetReplacement', () => {
+  // Regression test for #22304: when the asset placeholder sits inside a
+  // string literal and is preceded by a unary operator (typeof, void, !,
+  // delete), the bare `"+runtime+"` substitution produces output that
+  // parses as `(typeof "") + runtime + ""` instead of evaluating typeof
+  // over the concatenated string. The fix wraps in parens.
+  function rewrite(code: string, runtime: string): string {
+    const s = new MagicString(code)
+    assetUrlRE.lastIndex = 0
+    let match: RegExpExecArray | null
+    while ((match = assetUrlRE.exec(code))) {
+      writeRuntimeAssetReplacement(s, code, match, match[0], runtime)
+    }
+    return s.toString()
+  }
+
+  test('wraps quoted placeholder so typeof binds to the runtime expression', () => {
+    const out = rewrite(
+      'if (typeof "__VITE_ASSET__abc__" === "string") {}',
+      'new URL("./hero.png", import.meta.url).href',
+    )
+    expect(out).toBe(
+      'if (typeof (""+new URL("./hero.png", import.meta.url).href+"") === "string") {}',
+    )
+  })
+
+  test('uses parens when single quotes wrap the placeholder exactly', () => {
+    const out = rewrite("var x = '__VITE_ASSET__abc__'", 'r()')
+    expect(out).toBe('var x = (""+r()+"")')
+  })
+
+  test('uses parens when backticks wrap the placeholder exactly', () => {
+    const out = rewrite('var x = `__VITE_ASSET__abc__`', 'r()')
+    expect(out).toBe('var x = (""+r()+"")')
+  })
+
+  test('falls back to the legacy substitution outside string contexts', () => {
+    // CSS-in-JS shape: the placeholder is inside a string but immediately
+    // adjacent to non-quote characters (url(...) wrapper).
+    const out = rewrite(
+      'var s = ".foo{background:url(__VITE_ASSET__abc__)}"',
+      'r()',
+    )
+    expect(out).toBe('var s = ".foo{background:url("+r()+")}"')
+  })
+
+  test('does not pair mismatched surrounding quotes', () => {
+    // before='"' and after="'" should NOT be treated as a wrapped string,
+    // so the bare substitution applies and the surrounding chars stay.
+    const out = rewrite(`var x = "__VITE_ASSET__abc__'`, 'r()')
+    expect(out).toBe(`var x = ""+r()+"'`)
+  })
+})
diff --git a/packages/vite/src/node/plugins/asset.ts b/packages/vite/src/node/plugins/asset.ts
index 102e1c3125d2a3..7b4105ee0553d8 100644
--- a/packages/vite/src/node/plugins/asset.ts
+++ b/packages/vite/src/node/plugins/asset.ts
@@ -73,6 +73,34 @@ export function registerCustomMime(): void {
   mrmime.mimes.eot = 'application/vnd.ms-fontobject'
 }
 
+// When the placeholder sits inside a string literal (`"__VITE_ASSET__abc__"`),
+// expand the rewrite range to include the surrounding quotes and emit a
+// parenthesized string expression. Without parentheses, a leading unary
+// operator like `typeof "..."` parses as `(typeof "") + runtime + ""`,
+// which evaluates to a concatenated string instead of `"string"`. See #22304.
+// Exported for unit testing only.
+export function writeRuntimeAssetReplacement(
+  s: MagicString,
+  code: string,
+  match: RegExpExecArray,
+  full: string,
+  runtime: string,
+): void {
+  const start = match.index
+  const end = match.index + full.length
+  const before = code[start - 1]
+  const after = code[end]
+  if (
+    (before === '"' && after === '"') ||
+    (before === "'" && after === "'") ||
+    (before === '`' && after === '`')
+  ) {
+    s.update(start - 1, end + 1, `(""+${runtime}+"")`)
+  } else {
+    s.update(start, end, `"+${runtime}+"`)
+  }
+}
+
 export function renderAssetUrlInJS(
   pluginContext: PluginContext,
   chunk: RenderedChunk,
@@ -111,11 +139,15 @@ export function renderAssetUrlInJS(
       'js',
       toRelativeRuntime,
     )
-    const replacementString =
-      typeof replacement === 'string'
-        ? JSON.stringify(encodeURIPath(replacement)).slice(1, -1)
-        : `"+${replacement.runtime}+"`
-    s.update(match.index, match.index + full.length, replacementString)
+    if (typeof replacement === 'string') {
+      s.update(
+        match.index,
+        match.index + full.length,
+        JSON.stringify(encodeURIPath(replacement)).slice(1, -1),
+      )
+    } else {
+      writeRuntimeAssetReplacement(s, code, match, full, replacement.runtime)
+    }
   }
 
   // Replace __VITE_PUBLIC_ASSET__5aA0Ddc0__ with absolute paths
@@ -136,11 +168,15 @@ export function renderAssetUrlInJS(
       'js',
       toRelativeRuntime,
     )
-    const replacementString =
-      typeof replacement === 'string'
-        ? JSON.stringify(encodeURIPath(replacement)).slice(1, -1)
-        : `"+${replacement.runtime}+"`
-    s.update(match.index, match.index + full.length, replacementString)
+    if (typeof replacement === 'string') {
+      s.update(
+        match.index,
+        match.index + full.length,
+        JSON.stringify(encodeURIPath(replacement)).slice(1, -1),
+      )
+    } else {
+      writeRuntimeAssetReplacement(s, code, match, full, replacement.runtime)
+    }
   }
 
   return s