Can I debounce or throttle a watched <input> in AngularJS using _lodash?

Question

I have the following which does a watch on an field that\'s bound to $scope.id. Every time the input field value changes the watch function gets e

Answer 1

You can encapsulate this in a directive. Source: https://gist.github.com/tommaitland/7579618

<input type="text" ng-model="id" ng-debounce="1000">

Javascript

app.directive('ngDebounce', function ($timeout) {
  return {
      restrict: 'A',
      require: 'ngModel',
      priority: 99,
      link: function (scope, elm, attr, ngModelCtrl) {
          if (attr.type === 'radio' || attr.type === 'checkbox') {
              return;
          }

          var delay = parseInt(attr.ngDebounce, 10);
          if (isNaN(delay)) {
              delay = 1000;
          }

          elm.unbind('input');

          var debounce;
          elm.bind('input', function () {
              $timeout.cancel(debounce);
              debounce = $timeout(function () {
                  scope.$apply(function () {
                      ngModelCtrl.$setViewValue(elm.val());
                  });
              }, delay);
          });
          elm.bind('blur', function () {
              scope.$apply(function () {
                  ngModelCtrl.$setViewValue(elm.val());
              });
          });
      }
  };
});

Answer 2

You can use ngModelOptions in Angular 1.3.0

HTML:

<div ng-controller="Ctrl">
  <form name="userForm">
    Name:
    <input type="text" name="userName"
           ng-model="user.name"
           ng-model-options="{ debounce: 1000 }" />
    <button ng-click="userForm.userName.$rollbackViewValue(); user.name=''">Clear</button><br />
  </form>
  <pre>user.name = <span ng-bind="user.name"></span></pre>
</div>

More Info: https://docs.angularjs.org/api/ng/directive/ngModelOptions

Answer 3

Is that what are you looking for?

$scope.$watch("id", _.debounce(function (id) {
    // Code that does something based on $scope.id
    // This code will be invoked after 1 second from the last time 'id' has changed.
}, 1000));

Note, however, that if you want to change $scope inside that function you should wrap it $scope.$apply(...) as unless _.debounce function uses $timeout internally (which as far as I understand it doesn't do) Angular will not be aware of the changes you did on the $scope.

UPDATE

As to the updated question - yes you need to wrap the entire callback function body with

$scope.$apply():

$scope.$watch("id", _.debounce(function (id) {
    // This code will be invoked after 1 second from the last time 'id' has changed.
    $scope.$apply(function(){
        // Code that does something based on $scope.id
    })
}, 1000));

Answer 4

I know the question asks for a lodash solution. Anyway here is an angular only solution:

app.factory('debounce', function($timeout) {
    return function(callback, interval) {
        var timeout = null;
        return function() {
            $timeout.cancel(timeout);
            var args = arguments;
            timeout = $timeout(function () { 
                callback.apply(this, args); 
            }, interval);
        };
    }; 
}); 

In the controller:

app.controller('BlaCtrl', function(debounce) {

    $scope.$watch("id", debounce(function (id) {
        ....
    }, 1000));

});