Java script once alert

// Use function on page Without use return
function once_alert() {
  // Create variable for check alert status in browser
	var alertset = localStorage.getItem('alertset') || '';
	// if value not set in browser > local storage - run alert
  if (alertset != 'yes') {
    // write alert message in "txt"
		var txt = "Write once alert";
		alert(txt);
		localStorage.setItem('alertset','yes');
	}
}
//# My Edition From :
//# Reference : https://stackoverflow.com/questions/24768067/display-alert-only-once