What is the Solution to Prevent Angular from Clearing the Text Selection?

I'm facing a challenge with Angular where I need to render and refresh a complex list of objects every few seconds. The issue I have encountered is that during the refresh, even if a specific HTML subcomponent hasn't changed, the entire HTML is updated causing selected text (such as for copying) to be deselected.

I understand that altering HTML with an active selection poses an issue, but I'm curious to know if Angular offers a solution that I may not be aware of. Ideally, I would like only the HTML that has actually changed to be updated. While I could achieve this manually using jQuery, the manual approach is cumbersome in all other aspects.

JS:

angular.module('items', [])
.factory('itemList', ['$http', function($http) {
  var items = [];
  var refresh = function() {
    // HTTP call to fetch new list of items
    items.length = 0;
    for (var i = 0; i < 10; i++) {
      items.push("item " + Math.random(1, 10))
    }
  }
  refresh();
  return {
    items: items,
    refresh: refresh
  };
}]);


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

app.controller('ItemListController',
  ['$scope', 'itemList', '$interval',
  function($scope, itemList, $interval) {
    this.items = itemList.items;
    $interval(itemList.refresh, 2000)
  }
]);

HTML:

<body ng-app="app">
<div ng-controller="ItemListController as controller">
  <h3>Items</h3>
  <div ng-model="active">
    <div ng-repeat="item in controller.items">
        <div class="header">Header</div>
        <div>{{item}}</div>
        <hr/>
    </div>
  </div>
</div>

</body>

Answer №1

When itemList is completely replaced each time there's a refresh, Angular has no choice but to recreate all elements in the ng-repeat block. This may result in losing selection and can be costly for larger refreshes. To avoid this issue, consider implementing a merge function in your factory that compares the previous list with the new one and only adds or removes items as necessary without replacing the entire reference. This way, you only risk losing the selection if the item selected no longer exists.

If the list is lengthy and the changes from refresh to refresh are minimal, this approach will likely be more efficient.

Answer №2

When the $interval function is called, it refreshes the entire DOM causing the selection to be refreshed and displaying a new value. If you need to make a selection but want to cancel the interval for a specific period of time, you can use the $interval.cancel(milliseconds) method to pause the timer before restarting it with the desired range.

$scope.$watch("refresh", function(){
           $interval.cancel(5000);
          p = $interval(itemsList.refresh(), 2000);
        })

Answer №3

After some investigation, I finally cracked the code. Following Thor's lead led me in the right direction. The root of the issue lay in my neglect to include "track by FOO" within my ng-repeat. Without this key piece of information, AngularJS was unable to discern that the elements within my complex objects were the same and consequently triggered unnecessary redraws.

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