An Apple JXA script that toggles dark mode for the macOS desktop and Terminal

toggle-dark-mode.js

#!/usr/bin/osascript -l JavaScript

// Update these with your chosen themes for Apple Terminal
const TERMINAL_DARK_THEME_NAME = "YourDarkTheme"
const TERMINAL_LIGHT_THEME_NAME = "YourLightTheme"

const app = Application.currentApplication()
app.includeStandardAdditions = true

const SysEvents = Application("System Events")
const Terminal = Application("Terminal")
const darkTheme = Terminal.settingsSets.byName(TERMINAL_DARK_THEME_NAME)
const lightTheme = Terminal.settingsSets.byName(TERMINAL_LIGHT_THEME_NAME)

// What is the current setting?
const isDark = SysEvents.appearancePreferences().darkMode()

// Toggle it
SysEvents.appearancePreferences().darkMode = !isDark

// Select the associated mode for the terminal
let newSettings = darkTheme;
if (isDark) {
  newSettings = lightTheme
}

// Make sure new tabs and windows respect the new setting too
Terminal.defaultSettings = newSettings

// Update any open windows and tabs
for (let window of Terminal.windows()) {
  for (let tab of window.tabs()) {
    tab.currentSettings = newSettings
  }
}

console.log("Done.")