Kohjah Breese's solution isn't working to detect Brave on Android (e.g. Chrome is detected as Brave). But as he said If you search DuckDuckGo for [what's my user agent] they will return Brave. Then you can use the API of Duckduckgo to know if they browser is Brave :

var request = new XMLHttpRequest()



request.open('GET', 'https://api.duckduckgo.com/?q=useragent&format=json', true)



request.onload = function () {

  var data = JSON.parse(this.response)

  var isBrave = data['Answer'].includes('Brave');

  if(isBrave){

    console.log( isBrave );

  }

}



request.send()