GitHub-view_in_VSCode-.user.js

// ==UserScript==
// @name         View in VSCode
// @version      1.0
// @description  Option to view repository in online vscode instance
// @author       @aiexz
// @match        https://github.com/*
// @grant        None
// ==/UserScript==

(function() {
    //'use strict';

    var x = document.getElementsByClassName("file-navigation mb-3 d-flex flex-items-start");
    if (x.length){
        x = x[0]
        var btn = document.createElement("a")
        btn.className = "btn ml-2 d-none d-md-block"
        btn.href = window.location.href.replace("github.com", "github1s.com");
        btn.text = "VSCode online";
        x.insertBefore(btn, x.children[x.children.length -1]);
    }
})();

Created for https://github.com/conwnet/github1s