add share button for dartpad, for UserScript/ tampermonkey, you just add token for input

dartpad-share.js

// ==UserScript==
// @name         Shard in dartpad
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       Caijinglong
// @match        https://dartpad.cn/*
// @match        https://dartpad.dev/*
// @grant        none
// @require      https://code.jquery.com/jquery-3.4.1.min.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/clipboard.js/2.0.4/clipboard.min.js
// ==/UserScript==

// gist of the userscript: https://gist.github.com/CaiJingLong/a299d15b92edc2d09a8a06cf6dd5a1b0
let tokenKey = "githubToken";

function refreshToken() {
  window.githubToken = localStorage.getItem(tokenKey);
}

function tokenIsNull() {
  let githubToken = window.githubToken;
  console.log(`githubToken = ${githubToken}`);
  return (
    typeof githubToken == "undefined" ||
    githubToken == null ||
    githubToken === ""
  );
}

function saveToken(token) {
  localStorage.setItem(tokenKey, token);
}

function inputToken() {
  let token = prompt(
    "Enter your github access token for gist, which is stored in your localStorage and used to create gist. It will not be uploaded anywhere.",
    window.githubToken
  );
  console.log(`input token = ${token}`);
  if (!(typeof token == "undefined" || token === null || token === "")) {
    window.githubToken = token;
    saveToken(window.githubToken);
  }
}

function createButton(id, text) {
  let div = document.createElement("div");
  let button = document.createElement("button");
  button.innerText = text;
  button.id = id;
  button.className = "mdc-button mdc-ripple-upgraded";
  div.append(button);
  return div;
}

(function () {
  "use strict";

  refreshToken();
  if (tokenIsNull()) {
    inputToken();
  }
  let header = $("header")[0];

  header.append(createButton("custom_share", "Share to gist of github by userscript"));
  header.append(createButton("edit_token", "Edit github token"));
  header.append(createButton("test_share_api", "Test usability"));

  $("#custom_share").click(function () {
    // shared to 
    if (tokenIsNull()) {
      inputToken();
    }
    if (tokenIsNull()) {
      alert("Cannot share, please check your token");
      return;
    }

    share();
  });

  $("#edit_token").click(function () {
    inputToken();
  });

  $("#test_share_api").click(function () {
    testShareToken();
  });
})();

function share() {
  let button = $("#custom_share");
  button.attr("disabled", "true");

  let data = JSON.parse(localStorage.getItem("gist"));
  data.description = prompt("title for share");
  if (!data.description) {
    data.description = "share by dartpad";
  }

  data.files["README.md"] = {
    content: "Create by https://gist.github.com/CaiJingLong/a299d15b92edc2d09a8a06cf6dd5a1b0",
  };

  $.ajax({
    url: "https://api.github.com/gists",
    method: "POST",
    headers: {
      Authorization: `token ${window.githubToken}`
    },
    contentType: "application/json",
    data: JSON.stringify(data),
    dataType: "json",
    success: function (event) {
      let id = event.id;
      let shareUrl = `https://dartpad.cn/${id}`;
      copyText(shareUrl);
      alert(`share url: https://dartpad.cn/${id}\ngist url: ${event.html_url}`);
      button.removeAttr("disabled");
    },
    error: function (err) {
      if (err.status !== 200) {
        alert("The token is incorrect, it cannot access your gist.");
      } else {
        alert("The token is correct and can be shared normally.");
      }
      button.removeAttr("disabled");
    }
  });
}

function testShareToken() {
  $.ajax({
    url: "https://api.github.com/gists/starred",
    method: "GET",
    headers: {
      Authorization: `token ${window.githubToken}`
    },
    success: function (event) {
      alert("The token is correct and can be shared normally.");
    },
    error: function (err) {
      if (err.status !== 200) {
        alert("The token is incorrect, it cannot access your gist.");
      } else {
        alert("The token is correct and can be shared normally");
      }
    }
  });
}

function copyText(text) {
  let copyText = document.createElement("textarea");
  copyText.innerHTML =
    '<textarea readonly id="copy_text" style="position:absolute;left:-9999px"></textarea>';

  document.body.append(copyText);

  copyText.innerHTML = text;
  copyText.readOnly = false;
  copyText.select();
  copyText.setSelectionRange(0, copyText.value.length);
  document.execCommand("copy");
  copyText.readOnly = true;
  copyText.remove();
}