@naturalcycles/js-lib/dist/decorators/swarmSafe.decorator.js

Standard library for universal (browser + Node.js) javascript

import { _getTargetMethodSignature } from './decorator.util.js';
/**
 * Prevents "swarm" of async calls to the same method.
 * Allows max 1 in-flight promise to exist.
 * If more calls appear, while Promise is not resolved yet - same Promise is returned.
 *
 * Does not support `cacheKey`.
 * So, the same Promise is returned, regardless of the arguments.
 */
// eslint-disable-next-line @typescript-eslint/naming-convention
export const _SwarmSafe = () => (target, key, descriptor) => {
    if (typeof descriptor.value !== 'function') {
        throw new TypeError('@_SwarmSafe can be applied only to methods');
    }
    const originalFn = descriptor.value;
    const keyStr = String(key);
    const methodSignature = _getTargetMethodSignature(target, keyStr);
    const instanceCache = new Map();
    console.log('SwarmSafe constructor called', { key, methodSignature });
    // eslint-disable-next-line @typescript-eslint/promise-function-async
    descriptor.value = function (...args) {
        console.log('SwarmSafe method called', { key, methodSignature, args });
        const ctx = this;
        let inFlightPromise = instanceCache.get(ctx);
        if (inFlightPromise) {
            console.log(`SwarmSafe: returning in-flight promise`);
            return inFlightPromise;
        }
        console.log(`SwarmSafe: first-time call, creating in-flight promise`);
        inFlightPromise = originalFn.apply(ctx, args);
        instanceCache.set(ctx, inFlightPromise);
        void inFlightPromise.finally(() => {
            console.log(`SwarmSafe: in-flight promise resolved`);
            instanceCache.delete(ctx);
        });
        return inFlightPromise;
    };
};