Inject CSS into a Discord client.

injectUserCss.js

/*
 * Usage
 *
 * copy core.asar from Discord app
 *  Win: %APPDATA%/discord/0.0.xxx/modules/discord_desktop_core/core.asar
 *  Mac: ~/Library/Application\ Support/discord/0.0.xxx/modules/discord_desktop_core/core.asar
 * yarn add asar
 * asar e core.asar core
 * CSS_PATH=C:/dropbox/discordUser.css node injectUserCss.js
 * asar p core core.asar
 * copy core.asar to Discord app
 *
 * Supported: 0.0.250(Mac), 0.0.300(Win)
 */
const fs = require('fs');
const jsPath = 'core/app/mainScreen.js';

let content = fs.readFileSync(jsPath, 'utf-8');

const cssInjection = `
  require('fs').readFile('${process.env.CSS_PATH}', 'utf-8', (err, userCss) => {
    const style = document.createElement('style');
    style.innerHTML = userCss;
    document.head.appendChild(style);
  });
`;

content = content.replace('mainWindow.webContents.', `mainWindow.webContents.on('dom-ready', () => {
  mainWindow.webContents.executeJavaScript(\`${cssInjection}\`);
});mainWindow.webContents.`);

fs.writeFileSync(jsPath, content);