Reliably detect Brave Browser with native JS

checkIsBrave.js

// helper to find Brave in User Agent string
function isBraveAgent(userAgentResponse) {
	var isBraveIndex = ~userAgentResponse.indexOf('Brave')
	if (isBraveIndex < 0) {
		return true
	}
	return false
}

// Function from Javarome
// https://stackoverflow.com/questions/3760319/how-to-force-a-program-to-wait-until-an-http-request-is-finished-in-javascript
function httpRequest(address, reqType, asyncProc) {
  var req = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject("Microsoft.XMLHTTP");
  if (asyncProc) { 
    req.onreadystatechange = function() { 
      if (this.readyState == 4) {
        asyncProc(this);
      } 
    };
  } 
  req.open(reqType, address, !(!asyncProc));
  req.send();
  return req;
}

// Check reflected User Agent from whitelisted website (duckduckgo.com)
function checkIsBrave() {
	var isBraveBrower = false
	var req = httpRequest("https://api.duckduckgo.com/?q=whats+my+user+agent&format=json&pretty=1", "GET");
	var duckDuckResponse = JSON.parse(req.responseText)
	var userAgentResponse = duckDuckResponse["Answer"]
	var foundBraveInUserAgent = isBraveAgent(userAgentResponse)
	if (foundBraveInUserAgent){
		isBraveBrower = true
	}
	return isBraveBrower
}

checkIsBrave()