SOURCE

document.querySelector("#version").addEventListener("input", (e) => {
    const version = e.target.value;
    const value =
        '6' +
        version
            .split(".")
            .map((v, i) => Number(v).toString(16).padStart(i === 0 ? 1 : 2, '0'))
            .join("")
        ;
    document.querySelector("#value").innerText = value;
});

document.querySelector("#version").dispatchEvent(new Event("input"));

<a href="https://www.ez4leon.top/archives/skip-wechat-version-check" target="_blank">跳过微信过低版本的解决办法</a>
<div>微信版本号：</div>
<input placeholder="请输入" id="version" value="3.9.10.19" />
<div>数值：</div>
<div id="value"></div>

body {
    font-size: 20px;
}

input {
    width: 100%;
    line-height: 30px;
    font-size: 20px;
}