js how to get the browser zoom ratio

function getZoom(){
     
  let ratio = 0,
    screen = window.screen,
    ua = navigator.userAgent.toLowerCase();

  if (window.devicePixelRatio !== undefined) {
    
      ratio = window.devicePixelRatio;
  } else if (~ua.indexOf('msie')) {
      
    if (screen.deviceXDPI && screen.logicalXDPI) {
    
      ratio = screen.deviceXDPI / screen.logicalXDPI;
    }
  } else if (window.outerWidth !== undefined && window.innerWidth !== undefined) {
    
    ratio = window.outerWidth / window.innerWidth;
  }
  
   if (ratio){
    
    ratio = Math.round(ratio * 100);
  }
  
   return ratio;
};