Result

コード見せたいけどSyntax highlight使うほどじゃない時とかに。gistでいいんじゃ、と言われたらそれまでですが。

jQuery

;(function ( $, window, document, undefined ) {
    'use strict';

    var pluginName = 'lineLine',
        defaults = {
            startsFrom: 0,
            className: 'lineline'
        };
     //オプションセッティング
    function Plugin( element, options ) {
        this.element = element;
        this.options = $.extend( {}, defaults, options);

        this._defaults = defaults;
        this._name = pluginName;

        this.init();
    }

    Plugin.prototype.init = function () {
        var self = this;
        
        var lines = $(self.element).html().split('\n');
        var lineCount = lines.length;
        //textareaをtableにする
        var html = '<div class="' + self.options.className + '"><table class="' + self.options.className + '-code" border="0" cellspacing="0" cellpadding="0">';
        //ナンバリング
        for (var i = self.options.startsFrom; i < lineCount; i++){
            html += '<tr><td class="' + self.options.className + '-numbers">' + (i + 1) + '</td><td class="' + self.options.className + '-lines">' + lines[i] + '</td></tr>';
        }
        html += '</table></div>';
        
        $(self.element).before(html);
        $(self.element).remove();
    };

    $.fn[pluginName] = function ( options ) {
        return this.each(function () {
            if (!$.data(this, 'plugin_' + pluginName)) {
                $.data(this, 'plugin_' + pluginName,
                new Plugin( this, options ));
            }
        });
    };

})( jQuery, window, document );
//textareaを指定
$('textarea').lineLine();

css

.lineline{ 
max-height: 300px; 
width: 700px; 
margin: 50px auto 0; 
background: #ececec; 
padding: 20px; 
overflow: auto; 
text-align: left; 
}

.lineline-numbers   { 
width: 20px; 
border-right: 1px solid #ccc; 
padding-right: 
5px; color: #777; 
}
.lineline-lines{ 
padding-left: 20px; 
white-space: pre; 
white-space: -moz-pre; 
white-space: -pre; 
white-space: -o-pre; 
word-wrap: break-word; 
} 
.lineline-code{ 
font-family: 'Consolas'; 
font-size: 12px; 
line-height: 18px; 
width: 100%; 
white-space: nowrap; 
}

html

foobar<br /> hogehuga

via

add line number to textarea or code or any dom element lineLine