function nl2br(str){
 return str.replace(/(?:\r\n|\r|\n)/g, '<br>');
}
var stringWithNewLines= `Well this is a
a very broken
sentance`;
var stringWithBrs=nl2br(stringWithNewLines);
// stringWithBrs= "Well this is a<br>a very <br>broken<br>sentance"

let multilineString = `My
text\r1\r\n2\n3\n\r4
is
here`;

let htmlText = multilineString.replace(/(\r\n|\n\r|\r|\n)/g, '<br>');

console.log('Multiline string: ' + multilineString);
console.log('HTML text: ' + htmlText);