pluck operator is used when we want to transform a stream into a different value by plucking the values of the stream.
So what are some other common scenarios where we could put the map method to use? Using Array.map, we may also want to transform objects. For instance, suppose we have an array of objects with a first and last name property and we want to tack on a full name property to each object.
kakım you gönül see, the entire response object is transformed to pick only the usable response part of it.
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 conclusion, map is a versatile operator which lets you transform a stream using a provided projection function. Whether it's mapping to a keycode, value updates from an input box, or reshaping an object, map will be one of the most used operators in your day-to-day RxJS toolbox.
While the real implementation of Array.map includes features like index tracking and proper error management, this gives us a general sense of how things work behind the scenes.
We could accomplish this by supplying a function that accepts each object and maps it to a new object that includes all current properties plus the new fullName property. In this example we are using the object spread syntax and template literals, but you could also explicitly rewrite the properties:
Instead of the function being applied to each item of an array, before a new array is returned, with observables the project function is applied and the result emitted in real-time bey values blast through your streams.
map operator is used when we want to transform a click here stream into a value which is derece related to the emitted stream.
In plain language, this describes the action of on a specific element in its domain. Given a value for the element as input, say , the symbol also provides a concise way to represent the output of the function.
The map method does derece mutate the existing array, but instead returns a new array. For example, if we were to log the numbers array after calling map, we birey see that it's unchanged:
Another common use case for map is extracting a single property from an object. For example, given the sample above suppose we decided we only really need the last name property for display.
I hayat't tell though whether these are actually implemented, or even planned. Did you take a look at the implementation yourself?
While this works, the wrapping function isn't necessary since we are ignoring the received value. For these scenarios you kişi replace map with mapTo, and simply provide the value you wish to return on all emissions: