Differentiating the angular distinction between setting a variable with ng-click and invoking a function

Question

Differentiating the angular distinction between setting a variable with ng-click and invoking a function

I've encountered a situation like this before.

Let's assume the controller has these variables:

$scope.valueArr = ['Hello', 'No', 'Yes'];
$scope.myValue = 'Hello';

And there is an ng-repeat as follows:

<li ng-repeat="value in valueArr" ng-class="{'active' :  myValue == value}"><a>{{value}}</a> </li>

If I do this:

<a ng-click="myValue = value"> </a>

The new element gets the class, but the previous one loses it.

However, if I try this instead:

<a ng-click="setMyValue(value);"> </a>

and define the function in the controller:

$scope.setMyValue = function(value){$scope.myValue = value}

Only the last clicked element stays active, showing that a function is necessary for re-rendering. Can someone explain why this happens and when to use each method?

This case is just one example where re-rendering issues come up.

javascript angularjs angularjs-ng-click

Answer 1

Answer №1

One reason for this behavior is that when using ng-repeat, a new child scope is created for each repetition, as explained in the documentation.

This means that each repeated item has its own separate scope.

There is a distinct child scope for the first repetition.

There is a distinctive child scope for the second repetition.

There is a unique child scope for the third repetition.

...and so on.

Therefore, if you try to access a variable like (myValue) using

ng-click="myValue = value"

, Angular will search within the current repetition's child scope. If it doesn't find any existing reference to myValue, it will create one within that specific child scope. However, you can still access variables from the parent scope by using syntax like $parent.myValue.

You can test this behavior with the following demo.

Another approach to handle this situation is to use an object, for example:

$scope.tempObj = {myValue: 'Hello'};

Then, you can refer to this object property by using:

<a ng-click="tempObj.myValue = value">

Since myValue is now a property of the object tempObj, if Angular cannot find tempObj in the child scope, it will automatically look through the parent scopes.

If you opt to use a function like:

<a ng-click="setMyValue(value);"> </a>

&

$scope.setMyValue = function(value){$scope.myValue = value}

In the setMyValue function, it accesses $scope.myValue from the controller scope directly, rather than relying on the repeat's child scope.

Answer 2

One reason for this behavior is that when using ng-repeat, a new child scope is created for each repetition, as explained in the documentation.

This means that each repeated item has its own separate scope.

There is a distinct child scope for the first repetition.

There is a distinctive child scope for the second repetition.

There is a unique child scope for the third repetition.

...and so on.

Therefore, if you try to access a variable like (myValue) using

ng-click="myValue = value"

, Angular will search within the current repetition's child scope. If it doesn't find any existing reference to myValue, it will create one within that specific child scope. However, you can still access variables from the parent scope by using syntax like $parent.myValue.

You can test this behavior with the following demo.

Another approach to handle this situation is to use an object, for example:

$scope.tempObj = {myValue: 'Hello'};

Then, you can refer to this object property by using:

<a ng-click="tempObj.myValue = value">

Since myValue is now a property of the object tempObj, if Angular cannot find tempObj in the child scope, it will automatically look through the parent scopes.

If you opt to use a function like:

<a ng-click="setMyValue(value);"> </a>

&

$scope.setMyValue = function(value){$scope.myValue = value}

In the setMyValue function, it accesses $scope.myValue from the controller scope directly, rather than relying on the repeat's child scope.

Answer 3

Answer №2

The use of ng-repeat results in the creation of a distinct child scope for each repeated element. For instance, when you input

<a ng-click="myValue = value"> </a>

What occurs is the generation of a new variable 'myValue' within the child scope of the <li> after the user triggers the button. This action conceals the original value of 'myValue' within the parent scope without altering it - effectively causing all other <li> scopes to continue inheriting the original value from the parent scope.

On the contrary, if you were to write

<a ng-click="setMyValue(value);"> </a>

You would be directly invoking the function setMyValue that was established within the parent scope. Consequently, when the button is clicked, the setMyValue function executes and modifies the 'myValue' attribute within the parent scope. The child scope remains unaffected by this adjustment. With the alteration occurring within the parent scope, all instances of <li> elements inherit the updated value accordingly.

Answer 4

The use of ng-repeat results in the creation of a distinct child scope for each repeated element. For instance, when you input

<a ng-click="myValue = value"> </a>

What occurs is the generation of a new variable 'myValue' within the child scope of the <li> after the user triggers the button. This action conceals the original value of 'myValue' within the parent scope without altering it - effectively causing all other <li> scopes to continue inheriting the original value from the parent scope.

On the contrary, if you were to write

<a ng-click="setMyValue(value);"> </a>

You would be directly invoking the function setMyValue that was established within the parent scope. Consequently, when the button is clicked, the setMyValue function executes and modifies the 'myValue' attribute within the parent scope. The child scope remains unaffected by this adjustment. With the alteration occurring within the parent scope, all instances of <li> elements inherit the updated value accordingly.

Differentiating the angular distinction between setting a variable with ng-click and invoking a function

Answer №1

Answer №2

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