javascript - 为什么 AngularJS 过滤器只运行一次？

Question

考虑以下示例:

    angular.module('app', []).controller('TestController', function($scope) {
      $scope.getText = function() {
          console.log('getting text');
          return 'text';
      };
  }).filter('text', function() {
      return function() {
          console.log('text filter');
          return 'text';
      };
  });

 

  <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.2/angular.min.js"></script>
<div ng-app="app" ng-controller="TestController">
    <p>{{getText()}}</p>
    <p>{{'' | text}}</p>
</div>

请注意，getText() 函数运行两次，而过滤器仅运行一次。我假设 getText() 函数运行两次以确保模型现在稳定。为什么过滤器的行为不同？

Answer 1

关于这个主题的文档非常清楚:

In templates, filters are only executed when their inputs have changed. This is more performant than executing a filter on each $digest as is the case with expressions.

Here's the source.