Source for the sf.virtualScroll module for AngularJS

Intended as a replacement for ng-repeat for large collections of data and contains different solutions to the problem.

The module was originally developed as a proof of concept but has matured into a useable component. It isn't the ideal solution to the performance issues of large ng-repeat instances, but it does work as a drop-in replacement (with some caveats).

It started because I needed to display log messages and I didn't want to use paging. There were some excellent alternatives including some wrappers of jQuery grids, but nothing was using the ng-repeat pattern. I wrote a couple of articles explaining myself as I went along:

• https://stackfull.github.io/blog/2013/02/16/angularjs-virtual-scrolling-part-1.html
• https://stackfull.github.io/blog/2013/03/24/angularjs-virtual-scrolling-part-2.html

There should be an online demo here: http://demo.stackfull.com/virtual-scroll/

2016: I don't get much time to add to this component unless there are serious bugs to fix. If you need more features, there is a similar component https://github.com/kamilkp/angular-vs-repeat that uses a nicer directive structure in that the custom directive surrounds a vanilla ng-repeat to define the viewport. Although this relies on internals of ng-repeat, it is a better user experience. Also, more features are added and updates are frequent.

Whether you build the component, copy the raw source or use bower (see below), the end result should be included in your page and the module sf.virtualScroll included as a dependency:

angular.module('myModule', ['sf.virtualScroll']);

Then use the directive sf-virtual-repeat just as you would use ng-repeat.

<div class="viewport">
  <div>
    <table>
      <tbody>
        <tr sf-virtual-repeat="line in book.lines"><th>{{$index}}: <td>{{line}}
    </table>
  </div>
</div>

<div class="viewport real">
  <ul>
    <li ng-repeat="thing in simpleList">{{thing}}</li>
  </ul>
</div>

If you want to expose the scroll postion (to simulate an atEnd event for example), use ng-model and you have access to the scroll properties.

Check out the examples in the demo folder for all the details.

First up, the obligatory warning: virtual scrolling is usually the wrong approach. If you want to display really large lists, your users will probably not thank you for it: filtering can be a more friendly way to tame the data. Or if you have performance problems with angular bindings, one of the "bind-once" implementation may make more sense.

Tables are problematic. It is possible to use sf-virtual-repeat in a <tr> to create table rows, but you have to be very careful about your CSS.

The element having the sf-virtual-repeat needs to be contained within an element suitable for use as a viewport. This suitability is the main difficulty as the viewport must contain a single element (and no text) and this contained element must be explicitly sizable. So a table will need 2 parent divs for example.

The collection must be an array (not an object) and the array must not change identity - that is, the value on the scope must remain the same and you should push, pop, splice etc. rather than re-assigning to the scope variable. This is a limitiation that might be removed in future versions, but for now it's a consequence of watching the collection lightly.

Grunt is used as the build tool, so you will need node and npm installed. Since v0.4, grunt has 2 parts: the heavy lifting package grunt and the shell command grunt-cli. If you haven't already installed grunt-cli globally, do so now with:

sudo npm install -g grunt-cli

To run the simple demo, install the npm dependencies for the build tools and go:

npm install
grunt demo

You can now view the demo at http://localhost:8000/

Build with grunt dist and choose a file from the dist directory.

For use with bower, there is a separate repo containing just the built artifacts here: angular-virtual-scroll-bower. You can add the component to your project with:

bower install angular-virtual-scroll

Or by adding a line to your component.json file.

If you are using grunt for your build, consider using a plugin like bowerful.

All comments to [email protected]

• added sfVirtualScroll constant for version info
• [FIX #25] Guard against empty collection

• [ENHANCEMENT #13] reduce debug noise
• upgrade dependencies

• [ENHANCEMENT #9] allow filters in the collection expression
• [FIX #12] improved stability in the face of collection changes

• [FIX #6] be more careful searching for a viewport (tables again)
• [ENHANCEMENT #2]configurable watermark levels
• more demos

• [ENHANCEMENT #4] prevent tables messing up the viewport
• expose state variables as models

• added "auto-scroll" feature to the virtual repeater
• fleshed out demos in place of tests

First "dagnamit" fix.

First sight of daylight.