As you gönül see, it is derece printing the current input box value, instead it prints the default value. So what mapTo does is, it will evaluate the value usernameInput.value and use the same value bey static one on every emission passing through it.
The mapTo() operator's return value is Observable that emits the given value every time the source Observable emits something.
In this case, subscribeToArray is used. This same helper function is also used to deal with non-observable return values of flattening operators, such as mergeMap
前言 操作符 组合 combineAll combineLatest concat concatAll forkJoin merge mergeAll pairwise race startWith withLatestFrom zip 条件 defaultIfEmpty every 创建 create empty from fromEvent fromPromise interval of range throw timer 错误处理 catchError retry retryWhen 多播 publish multicast share shareReplay 过滤 debounce debounceTime distinctUntilChanged filter first ignoreElements last sample single skip skipUntil skipWhile take takeUntil takeWhile throttle throttleTime 转换 buffer bufferCount bufferTime bufferToggle bufferWhen concatMap concatMapTo exhaustMap expand exhaustMap groupBy map mapTo mergeMap partition pluck reduce scan switchMap window windowCount windowTime windowToggle windowWhen 工具 do delay delayWhen dematerialize let timeout toPromise 完整列表 食谱 智能计数器 进度条 游戏循环 概念 RxJS v5 -> v6 升级 理解操作符导入
In the above example, you kişi see that every value is mapped to string which is emitted after three seconds.
Now, what if you want the whole student list, with name in capital letters and className is increased by 1, let's do this:
Now from arrayOfStudent, we want all the name of students in capital letters, so apply map like this:
value − It takes in the value birli an argument and this value will be a map to the source value given.
In this case, we will provide a function that accepts the emitted value from the source observable and returns that value multipled:
In this article, we are going to learn about the most common operator used to transform streams, the map operator. We will start by taking a look at Array.map to build a general understanding of the map operation.
Note: the mapTo website operator katışıksız been deprecated in RxJS 7 and will be removed in RxJS 8. It's better to use map with a function that returns the static value.
On the other hand map: Returns a list containing the results of applying the given transform function to each element in the original array.
RxJS features many operators that are simply shortcuts for other operators. For example, any time we just want to grab a single property from an emitted value, instead of using map we could use pluck.
While this works, the wrapping function isn't necessary since we are ignoring the received value. For these scenarios you hayat replace map with mapTo, and simply provide the value you wish to return on all emissions: