Internet Archive Infinite Scroller

This is an infinite scroller web component, created with Lit. It detects when the user scrolls near the bottom to allow the consumer to fetch more data. It makes efficient use of browser resources by removing cells that are offscreen and loading a buffer of around either end of the visible cells to to preload cells before scrolling them into view.

Usage

// Have your component or a standalone datasource object
// implement the `InfiniteScrollerCellProviderInterface`,
// which has 1 method: `cellForIndex(index: number): TemplateResult | undefined`
class MyElement extends LitElement implements InfiniteScrollerCellProviderInterface {
  // infinite-scroller will call your method when it needs a cell at a given index
  cellForIndex(index: number): TemplateResult | undefined {
    const useTile1 = Math.random() < 0.5;
    if (useTile1) {
      return html`<tile-1>${index}</tile-1>`;
    } else {
      return html`<tile-2>${index}</tile-2>`;
    }
  }

  // when the user has scrolled to a certain point, it will emit a
  // `scrollThresholdReached` event, at which point you can fetch
  // more data and increase the `itemCount`
  scrollThresholdReached() {
    this.infiniteScroller.itemCount += 50;
  }

  // using infinite-scroller:
  // - `itemCount`: update this value when you want to display more data
  // - `cellProvider`: the data source for the cells that will have `cellForIndex(index:number)`
  // - `placeholderCell`: provide it a custom placeholder cell if you'd like
  // - `@scrollThresholdReached`: a listener for when the user nears the bottom to fetch more
  render() {
    return html`
      <infinite-scroller
        .itemCount=${100}
        .cellProvider=${this}
        .placeholderCellTemplate=${html`
          <my-placeholder-cell></my-placeholder-cell>
        `}
        @scrollThresholdReached=${this.scrollThresholdReached}
      >
      </infinite-scroller>
    `
  }
}

Local Demo with web-dev-server

yarn start

To run a local development server that serves the basic demo located in demo/index.html

Testing with Web Test Runner

To run the suite of Web Test Runner tests, run

yarn run test

To run the tests in watch mode (for <abbr title="test driven development">TDD</abbr>, for example), run

yarn run test:watch

Linting with ESLint, Prettier, and Types

To scan the project for linting errors, run

yarn run lint

You can lint with ESLint and Prettier individually as well

yarn run lint:eslint

yarn run lint:prettier

To automatically fix many linting errors, run

yarn run format

You can format using ESLint and Prettier individually as well

yarn run format:eslint

yarn run format:prettier

Tooling configs

For most of the tools, the configuration is in the package.json to reduce the amount of files in your project.

If you customize the configuration a lot, you can consider moving them to individual files.