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Synchronous lazy loader to load big list any or kind of that! In Ember Land ❤
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Sloth will help you to load a huge list lazily. You can lazy load your data using either of the below technique

Perfectly lightweight - 130B Min + GZip. Play around with the demo

Why Sloth?

Sloth is meant for his slowness. Is that the reason? No, the reason is, we are going to make him a lot faster 😉


Sloth will give you a property dataForCurrentView to loop over the passed data. Since Ember 🐹 will do the heavy weight-lifting for us by efficiently loading the list using each helper, you can relax and sit back!

Additionally, you can pass loadCount and initialDataCount to customize the initial load.

  • initialDataCount : How many items should Sloth render on initial load. Defaults to 20
  • loadCount : How many items should the Sloth load on reaching the threshold (2/3 of the current list length). Defaults to 10

On Scroll into the list

Since Sloth will watch the scroll event on a list container to lazy load the data, make sure you create a container manually with the id attribute as slothScroll (or anything of your choice) and specify the definite height. If your container has the id other than slothScroll, then pass the name of the id attribute (to bind action) as an argument, scrollContainer:

{{!-- template.hbs --}}
  as |sloth|

  <div id="postContainer" class="post-container"> {{!-- container --}}
    {{#each sloth.dataForCurrentView as |post|}}
      {{pretty-post post=post}}

/* app.css */
.post-container {
  height: 75vh;

NOTE: If your data should be load highly on demand (on scroll) like a facebook feed. This option will be the apt one. If you don't have a specific use case and the only requirement is to defer the loading of a bulk list to avoid janky pages, you should definitely try the background task method as it won't need any extra work from the host application side.

Background Tasks

This would be the most appropriate choice in most cases since it won't require any additional containers to create nor any style manipulations. The list will be loaded lazily on the window's requestIdleCallback. The event will be fired when the browser gets an idle relaxing time. It would be an appropriate time to load the remaining items onto the list. If the browser doesn't support requestIdleCallback then the data will be loaded using setTimeout with an interval time.

To use this method, we need to pass two arguments:

  • enableBackgroundLoad : Defaults to false
  • loadInterval : Denoted in ms and defaults to 200 (200ms). This serves two purposes:
    1. When the browser supports requestIdleCallback, then loadInterval will be used as a threshold time. If the event is not fired within the given time, data loading will be triggered forcefully.
    2. When the browser doesn't support requestIdleCallback and fell back to setTimeout, then this time will be used as a timeout for setTimeout.
{{!-- template.hbs --}}

  as |sloth|

  {{#each sloth.dataForCurrentView as |post|}}
    {{pretty-post post=post}}



Let's work together to make Sloth awesome:

  • Sloth has zero test. Need help in writing sophisticated tests.
  • Exploring Intersection Observer API for data load
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