记住打字稿中的可观察物 [英] Memoize for Observables in Typescript
本文介绍了记住打字稿中的可观察物的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我正在寻找实现非常昂贵的方法的最佳方法的最佳方法,该方法需要多个参数并返回一个Observable.有一种优雅的方法吗?
I am looking for the best way of implementing an optimization for very expensive method that takes multiple parameters and returns an Observable. Is there an elegant way of doing it?
我正在寻找的是这个的更漂亮的版本:
What I am looking for is prettier version of this:
class Example {
constructor(
private databaseService: DatabaseService,
private someService: SomeService)
expensive(param1: string, param2: string) : Observable<string> {
if (isMemoraized(param1,param2) {
return Observable.create(observer=>
observer.next(memorizedValue(param1, param2));
observer.complete();
} else {
return Observable.create(observer=>{
Observable.forkJoin([
this.databaseService.getValue(param1, param2),
this.someService.fetchDataFromServer(param2)].subscribe(
results => {
let result = results[0] + ' ' + results[1];
memorizeValue([param1,param2], result);
observer.next(result);
observer.complete();
});
});
}
}
}
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推荐答案
您可以创建一个装饰器以在运行时为每个装饰函数记住结果:
You can create a decorator to memoize the results in run-time for every decorated function:
function Memoized() {
return function(
target: any,
propertyKey: string,
descriptor: PropertyDescriptor
) {
const method = descriptor.value; // references the method being decorated
let cacheMember = propertyKey + "CacheMember";
// the Observable function
if (!descriptor.value) {
throw new Error("use MemoizeDecorator only on services methods");
}
descriptor.value = function(...args) {
if (!target[cacheMember]) {
let returnedObservable = method.apply(this, args);
if (!(returnedObservable instanceof Observable)) {
throw new Error(
`method decorated with Memoized Decorator must return Observable`
);
}
target[cacheMember] = returnedObservable.pipe(
publishReplay(),
refCount()
);
}
return target[cacheMember];
};
};
}
用法:
@Memoized()
expensive(param1: string, param2: string) : Observable<string> {
// ...the expensive task
}
警告! 装饰器是 js的阶段2提议! 不要在未转译代码的情况下使用修饰符(Typescript完全支持它)
Warning! Decorators are stage 2 proposal of js! Don't use decorators without transpiling your code (Typescript supports it completely)
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