Autogrow for textfields, as written by http://stackoverflow.com/users/21677/999 and posted in http://stackoverflow.com/questions/931207/is-there-a-jquery-autogrow-plugin-for-text-fields

autogrow.js

// From http://stackoverflow.com/questions/931207/is-there-a-jquery-autogrow-plugin-for-text-fields

(function ($) {
        $.fn.autoGrowInput = function (o) {

            o = $.extend({
                maxWidth:1000,
                minWidth:0,
                comfortZone:70
            }, o);

            this.filter('input:text').each(function () {

                var minWidth = o.minWidth || $(this).width(),
                        val = '',
                        input = $(this),
                        testSubject = $('<tester/>').css({
                            position:'absolute',
                            top:-9999,
                            left:-9999,
                            width:'auto',
                            fontSize:input.css('fontSize'),
                            fontFamily:input.css('fontFamily'),
                            fontWeight:input.css('fontWeight'),
                            letterSpacing:input.css('letterSpacing'),
                            whiteSpace:'nowrap'
                        }),
                        check = function () {

                            if (!input.val()) {
                                var placeholder = input.attr("placeholder");
//                                console.log("Using input placeholder as val: " + placeholder);
                                val = placeholder;
                            } else if (val === (val = input.val())) {
                                return;
                            }

                            // Enter new content into testSubject
                            var escaped = val.replace(/&/g, '&amp;').replace(/\s/g, '&nbsp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
                            testSubject.html(escaped);

                            // Calculate new width + whether to change
                            var testerWidth = testSubject.width(),
                                    newWidth = (testerWidth + o.comfortZone) >= minWidth ? testerWidth + o.comfortZone : minWidth,
                                    currentWidth = input.width(),
                                    isValidWidthChange = (newWidth < currentWidth && newWidth >= minWidth)
                                            || (newWidth > minWidth && newWidth < o.maxWidth);

                            // Animate width
                            if (newWidth > o.maxWidth) {
                                input.width(o.maxWidth);
                            } else if (isValidWidthChange) {
                                input.width(newWidth);
                            }

                        };

                testSubject.insertAfter(input);

                $(this).bind('keyup keydown blur update change', check);

            });

            return this;

        };

    })(jQuery);