Does handlebars.js replace newline characters with ?

It doesn’t do so automatically, but using the helpers feature this can be achieved:

JS:

Handlebars.registerHelper('breaklines', function(text) {
    text = Handlebars.Utils.escapeExpression(text);
    text = text.replace(/(\r\n|\n|\r)/gm, '<br>');
    return new Handlebars.SafeString(text);
});

HTML template:

<div>
    {{breaklines description}}
</div>