bahrus / be-lazy

be-lazy loads a template into the live DOM tree only when it becomes visible (or is about to be visible based on threshold settings.)

be-lazy

be-lazy loads a template into the live DOM tree only when it becomes visible (or is about to be visible based on threshold settings.)

Size of package, including custom element behavior framework (be-decorated):

Size of new code in this package:

The consumer of be-lazy needs to use css to set the size to something approximating what it will be when instantiated:

    <style>
        template[be-lazy], template[is-lazy]{
            display:block;
            height: 18px;
        }
    </style>
    <template be-lazy>
        <div>I am here</div>
    </template>

The role of be-lazy ends once it becomes viewable, and the content is instantiated. In fact, the template is deleted at that point.

Options include setting IntersectionObserverInit settings:

<template be-lazy='{
    "options": {
        "rootMargin": "0px",
        "threshold": "1.0"
    }
}'>

Other configuration settings include "enterDelay" and "exitDelay". The idea behind those settings is if the user is scrolling very quickly, it can slow the scrolling down if it is instantiating templates that have already zoomed past.

be-lazy can hold its own against content-visibility in terms of performance.

It is most effective if content is "paged" -- be-lazy really shouldn't hold a single div tag as shown above, but the amount of content inside should approximately fill the screen.

be-lazy is currently being used by one virtual list - xtal-vlist.

Support for doing transform during instantiation

There are two additional properties that the user can specify in order to perform a DTR-based transformation when the template appears within the view pane.

They are "transform" and "host". The host provider will need to carefully pass itself to the proxy behind the decorator via oTemplate.beDecorated.lazy.host. Both properties must be set in order for the template to be dynamically populated during instantiation.

Alternatively, the RenderContext can be passed via property ctx, so that the instantiated template can partake in reactive updates going forward.

[TODO] Support instantiating within shadow DOM

Viewing this element locally

Any web server than can serve static files will do, but...

1. Install git.
2. Fork/clone this repo.
3. Install node.
4. Open command window to folder where you cloned this repo.

5. npm install

6. npm run serve

7. Open http://localhost:3030/demo/dev in a modern browser.

Running Tests

> npm run test

Using from CDN:

<script type=module crossorigin=anonymous>
    import 'https://esm.run/be-lazy';
</script>

Referencing via ESM Modules:

import 'be-lazy/be-lazy.js';