Firefox 實作了 BigInt (進度可以在「Implementation of BigInt values for SpiderMonkey」這邊看到)：「bigint shipping in firefox!」，現在可以在 68 beta 版裡使用：
I am delighted to share with folks the results of a project I have been helping out on for the last few months: implementation of "BigInt" in Firefox, which is finally shipping in Firefox 68 (beta).
另外文中也提到了其他瀏覽器的情況 (再 Can I Use 也可以看到「BigInt」目前的支援情況)，用 V8 engine 的都已經支援 (包括 Chrome 與新版的 Edge)，而 Safari 也在實作中：
BigInt is also shipping already in V8 and Chrome, and my colleague Caio Lima has an project in progress to implement it in JavaScriptCore / WebKit / Safari. Depending on your target audience, BigInt might be deployable already!
另外一個有趣的事情是 license，其中馬上可以想到的是 GMP，裡面牽扯到 LGPLv3 與 GPLv2 的授權問題：
Since version 6, GMP is distributed under the dual licenses, GNU LGPL v3 and GNU GPL v2. These licenses make the library free to use, share, and improve, and allow you to pass on the result. The GNU licenses give freedoms, but also set firm restrictions on the use with non-free programs.
從說明有提到一些目標，短期可能會用 GMP 以儘快時做出合理的效能版本，長期則是希望用自己的版本：
An important design question is whether to implement the arithmetic operators as native or self-hosted intrinsics, probably using an external library such as GMP in the former case. Using an existing library has the advantage of providing good performance for less initial effort, but a self-hosted library also has advantages, such as greater flexibility in representation, better compiler integration, and simpler integration with the rest of the JS runtime (GC, etc.).
2018 年一月的討論有提到有一包 patch 是使用 GMP 的版本，這樣看起來應該是有解決 license 上的問題...
The current version of the patch uses libgmp for BigInt arithmetic, supports most features from the current proposal, and passes all up-to-date test262 tests for BigInt. Direct compiler support for BigInt has been removed; instead, compilation should fail if a possible BigInt value is encountered.
後續的描述裡面也都有提到 GMP 相關的事情，應該是沒錯...
