Auto Grow/Shrink textarea directive for AngularJS (credits to this gist https://gist.github.com/thomseddon/4703968, specially @huyttq)

autogrow.js

angular.module("myApp").directive("autoGrow", function(){
    return function(scope, element, attr){
        var update = function(){
            element.css("height", "auto");
            var height = element[0].scrollHeight;
            if(height > 0){
                element.css("height", height + "px");
            }
        };
        scope.$watch(attr.ngModel, function(){
            update();
        });
        attr.$set("ngTrim", "false");
    };
});

in case textarea is not yet visible:

if(!element.is(':visible')) {
  scope.$watch(function () { return element.is(':visible'); }, function (visible) {
    if(visible) {
      autogrow();
      scope.$applyAsync();
    }
  });
}