50 lines
1.9 KiB
JavaScript
50 lines
1.9 KiB
JavaScript
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// This takes advantage of `Promise.withResolvers` which is polyfilled in
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// this imported module.
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import "./polyfill-promise-with-resolvers";
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/**
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* A wrapper for a function that will only allow one call to the function to
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* execute at a time.
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*/ export class Batcher {
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constructor(cacheKeyFn, schedulerFn = (fn)=>fn()){
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this.cacheKeyFn = cacheKeyFn;
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this.schedulerFn = schedulerFn;
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this.pending = new Map();
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}
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static create(options) {
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return new Batcher(options == null ? void 0 : options.cacheKeyFn, options == null ? void 0 : options.schedulerFn);
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}
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/**
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* Wraps a function in a promise that will be resolved or rejected only once
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* for a given key. This will allow multiple calls to the function to be
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* made, but only one will be executed at a time. The result of the first
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* call will be returned to all callers.
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*
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* @param key the key to use for the cache
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* @param fn the function to wrap
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* @returns a promise that resolves to the result of the function
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*/ async batch(key, fn) {
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const cacheKey = this.cacheKeyFn ? await this.cacheKeyFn(key) : key;
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if (cacheKey === null) {
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return fn(cacheKey, Promise.resolve);
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}
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const pending = this.pending.get(cacheKey);
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if (pending) return pending;
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const { promise, resolve, reject } = Promise.withResolvers();
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this.pending.set(cacheKey, promise);
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this.schedulerFn(async ()=>{
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try {
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const result = await fn(cacheKey, resolve);
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// Resolving a promise multiple times is a no-op, so we can safely
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// resolve all pending promises with the same result.
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resolve(result);
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} catch (err) {
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reject(err);
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} finally{
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this.pending.delete(cacheKey);
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}
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});
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return promise;
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}
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}
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//# sourceMappingURL=batcher.js.map
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