What is the importance of using $scope.$apply after assigning values to ng-model within forms?

Question

What is the importance of using $scope.$apply after assigning values to ng-model within forms?

Let's talk about a form:

<form name="placeThis" id="placeThis" novalidate ng-submit="submitForm();">
    <input type="hidden" ng-model="placeThis.target"/>
</form>

My goal is to assign a default value to placeThis.target from my controller. Here is how I am trying to achieve it:

$scope.placeThis = { target: 0 }

However, this doesn't seem to work unless I use $scope.$apply or wrap it inside $timeout (which triggers $scope.$apply automatically).

I am able to save other $scope values from the controller without any issues, but for values within forms, I need to use $timeout or they are not retained on submit. Can you explain why this is the case?

javascript angularjs

Answer 1

Answer №1

Take a look at the demonstration below

Make sure to modify the name of your form from 'placeThis' to something like 'placeThisForm' to prevent overwriting the values of $scope.placeThis set in your controller.

Check out the demo below

var app = angular.module('app', []);

app.controller('homeCtrl', function($scope) {

  $scope.placeThis = {
    target: "One",
    name: "Tim"

  };


});

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>

<div ng-app="app">
  <div ng-controller="homeCtrl">
    <form name="placeThisForm" id="placeThis" novalidate ng-submit="submitForm();">
      <label>Target</label>
      <input type="text" ng-model="placeThis.target" />
      <label>Name</label>
      <input type="text" ng-model="placeThis.name" />
    </form>
  </div>
</div>

Answer 2

Take a look at the demonstration below

Make sure to modify the name of your form from 'placeThis' to something like 'placeThisForm' to prevent overwriting the values of $scope.placeThis set in your controller.

Check out the demo below

var app = angular.module('app', []);

app.controller('homeCtrl', function($scope) {

  $scope.placeThis = {
    target: "One",
    name: "Tim"

  };


});

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>

<div ng-app="app">
  <div ng-controller="homeCtrl">
    <form name="placeThisForm" id="placeThis" novalidate ng-submit="submitForm();">
      <label>Target</label>
      <input type="text" ng-model="placeThis.target" />
      <label>Name</label>
      <input type="text" ng-model="placeThis.name" />
    </form>
  </div>
</div>

Answer 3

Answer №2

It seems that the issue lies within the form name you are using. For more information on Angular forms, you can refer to the documentation here. According to the documentation:

If the name attribute is specified, the form controller is published onto the current scope under this name.

Therefore, a different object is stored under the specified name in the scope. You can try setting a different form name like this:

<form name="placeThisForm" id="placeThis" novalidate ng-submit="submitForm();">
    <input type="hidden" ng-model="placeThis.target"/>
</form>

In your controller, you can define it as:

$scope.placeThis = { target: 0 }

Another approach to set the initial value is by using ng-init:

<form name="placeThisForm" id="placeThis" novalidate ng-submit="submitForm();">
   <input ng-init="placeThis.target = 0" type="input"  ng-model="placeThis.target"/>
</form>

Answer 4

It seems that the issue lies within the form name you are using. For more information on Angular forms, you can refer to the documentation here. According to the documentation:

If the name attribute is specified, the form controller is published onto the current scope under this name.

Therefore, a different object is stored under the specified name in the scope. You can try setting a different form name like this:

<form name="placeThisForm" id="placeThis" novalidate ng-submit="submitForm();">
    <input type="hidden" ng-model="placeThis.target"/>
</form>

In your controller, you can define it as:

$scope.placeThis = { target: 0 }

Another approach to set the initial value is by using ng-init:

<form name="placeThisForm" id="placeThis" novalidate ng-submit="submitForm();">
   <input ng-init="placeThis.target = 0" type="input"  ng-model="placeThis.target"/>
</form>

What is the importance of using $scope.$apply after assigning values to ng-model within forms?

Answer №1

Check out the demo below

Answer №2

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