63 lines
2.5 KiB
TypeScript
63 lines
2.5 KiB
TypeScript
/**
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* Use as a Decorator on async functions, it will limit how many times the function can be
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* in-flight at a time.
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*
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* Calls beyond the limit will be queued, and run when one of the active calls finishes
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*/
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export function throttle(limit: number, throttleKey: (args: any[]) => string) {
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return <T>(target: any, propertyKey: string | symbol,
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descriptor: TypedPropertyDescriptor<(...args: any[]) => Promise<T>>) => {
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const originalMethod: () => Promise<T> = descriptor.value;
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const allThrottles = new Map<any, Map<string, (() => void)[]>>();
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const getThrottles = (obj: any) => {
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let throttles = allThrottles.get(obj);
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if (throttles != null) {
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return throttles;
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}
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throttles = new Map<string, (() => void)[]>();
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allThrottles.set(obj, throttles);
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return throttles;
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};
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return {
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value: function(...args: any[]) {
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const throttles = getThrottles(this);
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const argsThrottleKey = throttleKey(args);
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let queue = throttles.get(argsThrottleKey);
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if (queue == null) {
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queue = [];
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throttles.set(argsThrottleKey, queue);
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}
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return new Promise<T>((resolve, reject) => {
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const exec = () => {
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const onFinally = () => {
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queue.splice(queue.indexOf(exec), 1);
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if (queue.length >= limit) {
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queue[limit - 1]();
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} else if (queue.length === 0) {
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throttles.delete(argsThrottleKey);
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if (throttles.size === 0) {
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allThrottles.delete(this);
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}
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}
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};
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originalMethod.apply(this, args).then((val: any) => {
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onFinally();
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return val;
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}).catch((err: any) => {
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onFinally();
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throw err;
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}).then(resolve, reject);
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};
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queue.push(exec);
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if (queue.length <= limit) {
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exec();
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}
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});
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},
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};
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};
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}
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