Dynamically add new UserScript via an HTML button

Question

I'm making a website to post some scripts that I made, I would like to create a button on my page to dynamically install the UserScript with Tampermonkey or Greasemonkey, just like in Greasyfork.

Page example: Script example

Answer 1

You can try to trigger a download using a hidden <a> element with a download attribute set to the filename ending in .user.js. You might need to enable some settings in your browser to detect downloading opening of UserScripts.

Note: You may need to send the text to a server (PHP, Node, etc...), save the file as *.user.js and then create an <iframe> with an href poiting to the filename on the server to trigger a proper file download/install. When you install a script on Greasyfork, it downloads a *.user.js file that is hosted on their server(s). The filename that is downloaded fits the following the pattern:

https://greasyfork.org/scripts/<ID>-script-name/code/Script%20Name.user.js

Downloading scripts from the client or local file system is frowned upon in modern web dev.

const download = (content, mimeType, filename) => {
  const
    a = document.createElement('a'),
    blob = new Blob([content], {type: mimeType}),
    url = URL.createObjectURL(blob);
  a.setAttribute('href', url);
  a.setAttribute('download', filename);
  a.click();
  console.log(`Downloading: ${filename}`);
};

const extractFilenameFromScript = (script) => {
  const [, scriptName] = script.match(/^\/\/\s*@name\s+(.+)$/m);
  return `${scriptName.replace(/[^a-z0-9]+/ig, '-').toLowerCase()}.user.js`;
};

const downloadScript = () => {
  const script = document.querySelector('.user-script').textContent.trim();
  const filename = extractFilenameFromScript(script);
  download(script, 'text/javascript', filename);
};

document.querySelector('.download-btn').addEventListener('click', downloadScript);

.user-script {
  width: 100%;
  height: 8em;
}

<textarea class="user-script">// ==UserScript==
// @name         My Awesome Script
// @namespace    com.stackoverflow.questions
// @version      1.0.0
// @description  An example UserScript to download
// @author       Mr. Polywhirl
// @match        https://stackoverflow.com/questions/66428142
// @grant        none
// ==/UserScript==
(function() {
    'use strict';
    alert('Hello World');
})();
</textarea>
<button class="download-btn">Download</button>