ponepaste-load-from-file.user.js

// ==UserScript==
// @name         Ponepaste - load from file
// @version      0.0.1
// @author       Marker
// @license      WTFPL
// @namespace    https://github.com/marktaiwan/
// @match        https://ponepaste.org/
// @grant        none
// @inject-into  content
// @noframes
// ==/UserScript==

(function () {
'use strict';

const $ = (selector, parent = document) => parent.querySelector(selector);

function loadFromFile() {
  const filePicker = document.createElement('input');
  filePicker.type = 'file';

  filePicker.addEventListener('change', () => {
    const title = $('form[name="mainForm"] input[name="title"]');
    const textarea = $('form[name="mainForm"] textarea.form-control');
    if (!title || !textarea) return;

    const reader = new FileReader();
    const file = filePicker.files[0];
    const name = file.name.endsWith('.txt') ? file.name.slice(0, -4) : file.name;
    reader.readAsText(file);
    reader.onload = () => {
      title.value = name.trim();
      textarea.value = reader.result;
    };
  }, {once: true});

  filePicker.click();
}

function init() {
  const importButton = document.createElement('button');
  importButton.innerText = 'Load from file';
  importButton.style.marginBottom = '20px';
  importButton.addEventListener('click', loadFromFile);
  $('form[name="mainForm"]')?.before(importButton);
}

init();
})();