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 someone uses debounced model updates - this will just work with a timeout, which is not very nice, so i changed the code a bit to also listen to the input event:

angular.module('myApp').directive('autogrow', function () {
  return {
    restrict: 'A',
    link: function (scope, element, attrs) {
      // hide scroll of textarea
      element.css('overflow', 'hidden');

      var autogrow = function () {
        element.css('height', 'auto');

        var height = element[0].scrollHeight;

        if(height > 0){
          element.css('height', height + 'px');
        }
      };

      // using 'input' event on element, because of debounced model update
      element.on('input', autogrow);

      // need this too, for initialize
      scope.$watch(attrs.ngModel, autogrow);
    }
  };
});

@lpsBetty
Your trick of binding input event is great! Thanks.
PS:
I was implementing autogrowing textarea in ionic 1 modal template while I should consider a delay effect of modal opening. So I added a modal.shown watcher.

angular.module('myApp').directive('autogrow', function () {
  return {
    restrict: 'A',
    link: function (scope, element, attrs) {
      // hide scroll of textarea
      element.css('overflow', 'hidden');

      var autogrow = function () {
        element.css('height', 'auto');

        var height = element[0].scrollHeight;

        if(height > 0){
          element.css('height', height + 'px');
        }
      };

      // using 'input' event on element, because of debounced model update
      element.on('input', autogrow);

      // need this too, for initialize
      scope.$watch(attrs.ngModel, autogrow);

      /////////////////////////////////////////////////
      // apply after modal is shown <- ADD HERE
      scope.$on('modal.shown', autogrow);
    }
  };
});

Hope this might help someone.

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();
    }
  });
}