How do I get Tailwind’s active breakpoint in JavaScript?

From the tailwind docs, you can import your config from the tailwindcss node module:

import resolveConfig from 'tailwindcss/resolveConfig'
import tailwindConfig from './tailwind.config.js'

const fullConfig = resolveConfig(tailwindConfig)

fullConfig.theme.width[4]
// => '1rem'

fullConfig.theme.screens.md
// => '768px'

fullConfig.theme.boxShadow['2xl']
// => '0 25px 50px -12px rgba(0, 0, 0, 0.25)'

As you can see above, you can get your breakpoints by referencing fullConfig.theme.screens.{breakpoint}. You should be able to compare this to your current screen width using javascript.

Find the official tailwind description here.