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I'm trying out Angular custom filter example from: https://scotch.io/tutorials/building-custom-angularjs-filters#filters-that-actually-filter which in my version looks like:

<!DOCTYPE html>
<html>
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.4.8/angular.min.js"></script>
<body>

<div ng-app="myApp" ng-controller="demo" >

    <div>
      
                   <p><strong>Original:</strong></p>
                   <ul class="list">
                     <li ng-repeat="x in example1">{{ x.name }}</li>
                   </ul>
                   <p><strong>Static Language Filter:</strong></p>
                   <ul class="list">
                     <li ng-repeat="x in example1 | staticLanguage">{{x.name }}</li>
                   </ul>
               
      </div>

</div>

<script>
var app = angular.module('myApp', []);
var counter=0;

app.controller('demo', function($scope){  
  $scope.example1 = [
    {name: 'C#', type : 'static'},
    {name: 'PHP', type : 'dynamic'},
    {name: 'Go', type : 'static'},
    {name: 'JavaScript', type: 'dynamic'},
    {name: 'Rust', type: 'static'}
  ];
  
});


// Setup the filter
app.filter('staticLanguage', function() {  // Create the return function and set the required parameter name to **input**
  return function(input) {
    counter+=1;
    console.log(counter);    
    var out = [];
    // Using the angular.forEach method, go through the array of data and perform the operation of figuring out if the language is statically or dynamically typed.
    angular.forEach(input, function(input) {
      if (input.type === 'static') {       
        out.push(input);
      }      
    });    
    return out;

  };
});

</script>

</body>
</html>

It seems from console.log that for some reason custom filter function staticLanguage is called two times but from the code itself it is called only one time: ng-repeat="x in example1 | staticLanguage"

Anyone has any idea why?

P.S I've yet to figure out what does "dirty-checking" has to do with my question... if I remove counter variable and just put some console.log("text") in it's place staticLanguage function is still called two times

3 Answers3

2

As far as I am aware this is due to AngularJS dirty-checking and has been asnwered elsewhere here. This is normal, have a read of the link.

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David Cusack
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2

This is normal, angularjs uses a 'dirty-check' approach, so it needs to call all the filters to see if any changes exist. After this it detects that you have a change on one variable (the one that you typed) and then it re-executes all filters again to detect if it has other changes.

See the first answer of this question

How does data binding work in AngularJS?

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Himanshu sharma
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0

Well, I don't know if this will serve to you , but here's a snippet working that could be a possible solution for you:

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

app.controller('mainCtrl', function($scope) {
  $scope.languages = [  
    {  
      "name":"C#",
      "type":"static"
    },
    {  
      "name":"PHP",
      "type":"dynamic"
    },
    {  
      "name":"Go",
      "type":"static"
    },
    {  
      "name":"JavaScript",
      "type":"dynamic"
    },
    {  
      "name":"Rust",
      "type":"static"
    }
  ];
  
  $scope.static_languages = $scope.languages.filter(x => x.type == 'static');
  $scope.dynamic_languages = $scope.languages.filter(x => x.type == 'dynamic');
});
<!DOCTYPE html>
<html ng-app="app">

<head>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.7/angular.min.js">
</script>
</head>
<body ng-controller="mainCtrl">
  <div>
<p><strong>All languages:</strong></p>
<ul class="list">
  <li ng-bind="language.name" ng-repeat="language in languages"></li>
</ul>
<p><strong>Static Languages Filter:</strong></p>
<ul class="list">
  <li ng-bind="language.name" ng-repeat="language in static_languages"></li>
</ul>
<p><strong>Dynamic Languages Filter:</strong></p>
<ul class="list">
  <li ng-bind="language.name" ng-repeat="language in dynamic_languages"></li>
</ul>
  </div>
</body>
</html>
developer033
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