@o3r/core/utils/rendering/rendering.helpers.js

Core of the Otter Framework

import { animationFrameScheduler, from, observeOn, of, } from 'rxjs';
import { bufferCount, concatMap, delay, mergeMap, scan, tap, } from 'rxjs/operators';
/**
 * Buffers and emits data for lazy/progressive rendering of big lists
 * That could solve issues with long-running tasks when trying to render an array
 * of similar components.
 * @param delayMs Delay between data emits
 * @param concurrency Amount of elements that should be emitted at once
 */
export function lazyArray(delayMs = 0, concurrency = 2) {
    let isFirstEmission = true;
    return (source$) => {
        return source$.pipe(mergeMap((items) => {
            if (!isFirstEmission) {
                return of(items);
            }
            const items$ = from(items);
            return items$.pipe(bufferCount(concurrency), concatMap((value, index) => {
                return of(value).pipe(observeOn(animationFrameScheduler), delay(index * delayMs));
            }), scan((acc, steps) => {
                return [...acc, ...steps];
            }, []), tap((scannedItems) => {
                const scanDidComplete = scannedItems.length === items.length;
                if (scanDidComplete) {
                    isFirstEmission = false;
                }
            }));
        }));
    };
}
//# sourceMappingURL=rendering.helpers.js.map