CSS:
textarea {
resize: none;
min-height: 100px;
padding: 5px;
overflow: hidden;
box-sizing: border-box;
}
Script:
jQuery(document).ready(function($){
$('textarea').on('input', function(){
var minHeight = parseInt($(this).css('min-height'));
$(this).css('height', minHeight + 'px');
var scrollHeight = $(this).get(0).scrollHeight;
$(this).css('height', scrollHeight + 'px');
});
});