nl2br() equivalent in javascript [duplicate]

Take a look at nl2br on php.js which seems exactly what you're looking for. Basically, it's:

function nl2br (str, is_xhtml) {    if (typeof str === 'undefined' || str === null) {        return '';    }    var breakTag = (is_xhtml || typeof is_xhtml === 'undefined') ? '<br />' : '<br>';    return (str + '').replace(/([^>\r\n]?)(\r\n|\n\r|\r|\n)/g, '$1' + breakTag + '$2');}

EDIT:
your example using nl2br() may be changed like this:

$('#TextArea').keypress(function(evt){        $('#TextArea1').html(nl2br($('#TextArea').val()));    });

(note that this updates #TextArea1 on every keypress and doesn't change the value of #TextArea wich is what I think you're looking for, but I might be misunderstanding)

EDIT2:
If you want to get the behaviour of your old function (with inserting <br/>s to #TextArea) do this:

$('#TextArea').keypress(function(evt){        $('#TextArea').html(nl2br($('#TextArea').val())); // replace linebreaks first        $('#TextArea1').html($('#TextArea').val()); // copy to #TextArea1    });

Here is a function nl2br in php.js.

function nl2br (str, is_xhtml) {  // http://kevin.vanzonneveld.net  // +   original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)  // +   improved by: Philip Peterson  // +   improved by: Onno Marsman  // +   improved by: Atli Þór  // +   bugfixed by: Onno Marsman  // +      input by: Brett Zamir (http://brett-zamir.me)  // +   bugfixed by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)  // +   improved by: Brett Zamir (http://brett-zamir.me)  // +   improved by: Maximusya  // *     example 1: nl2br('Kevin\nvan\nZonneveld');  // *     returns 1: 'Kevin<br />\nvan<br />\nZonneveld'  // *     example 2: nl2br("\nOne\nTwo\n\nThree\n", false);  // *     returns 2: '<br>\nOne<br>\nTwo<br>\n<br>\nThree<br>\n'  // *     example 3: nl2br("\nOne\nTwo\n\nThree\n", true);  // *     returns 3: '<br />\nOne<br />\nTwo<br />\n<br />\nThree<br />\n'  var breakTag = (is_xhtml || typeof is_xhtml === 'undefined') ? '<br ' + '/>' : '<br>'; // Adjust comment to avoid issue on phpjs.org display  return (str + '').replace(/([^>\r\n]?)(\r\n|\n\r|\r|\n)/g, '$1' + breakTag + '$2');}