When working with ng-if in AngularJs, is it more efficient to evaluate the condition directly in the template or to invoke a function that will return a boolean value?

Question

When working with ng-if in AngularJs, is it more efficient to evaluate the condition directly in the template or to invoke a function that will return a boolean value?

<!-- template.html -->
<div ng-if="itemsExist(items)">
    <!-- content -->
</div>

<!-- controller.js -->
function itemsExist(itemsList) {
    return itemsList.length > 0;
}

vs

<!-- template.html -->
<div ng-if="$ctrt.hasItems()">
    <!-- content -->
</div>

<!-- controller.js -->
$ctrt.hasItems = (itemsList) => {
    return itemsList.length > 0;
};

Is it more effective to do the evaluation in JavaScript or directly in the HTML template?

javascript angularjs

Answer 1

Answer №1

The function in the second example runs multiple times because Angular may not detect changes to $scope values during each digest cycle, causing it to execute the function repeatedly. This happens when the ng-if conditions evaluate to true.

Check out this demo showcasing the behavior:

var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope) {
  $scope.items = [1, 2, 3];
  var x = 0;
  $scope.hasItems = function() {
    x++;
    console.log("execution", x);
    return $scope.items.length > 0;
  }
});

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.4/angular.min.js"></script>

<div ng-app="myApp" ng-controller="myCtrl">
  Test:
  <div ng-if="hasItems()">Has items</div>
</div>

It's recommended to initialize variables in the controller instead of using get methods/functions to check their values. Stick to the first approach where you directly check the variable.

Answer 2

The function in the second example runs multiple times because Angular may not detect changes to $scope values during each digest cycle, causing it to execute the function repeatedly. This happens when the ng-if conditions evaluate to true.

Check out this demo showcasing the behavior:

var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope) {
  $scope.items = [1, 2, 3];
  var x = 0;
  $scope.hasItems = function() {
    x++;
    console.log("execution", x);
    return $scope.items.length > 0;
  }
});

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.4/angular.min.js"></script>

<div ng-app="myApp" ng-controller="myCtrl">
  Test:
  <div ng-if="hasItems()">Has items</div>
</div>

It's recommended to initialize variables in the controller instead of using get methods/functions to check their values. Stick to the first approach where you directly check the variable.

When working with ng-if in AngularJs, is it more efficient to evaluate the condition directly in the template or to invoke a function that will return a boolean value?

Answer №1

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