What is pipe function in Angular

Question

Pipes are filters for transforming data  formats  in the template   I came across the pipe   function as below  What does this pipe   function exactly mean in this case    return this http get lt Hero gt  url     pipe      tap     gt  this log  fetched hero id   id          catchError this handleError lt Hero gt   getHero id   id

User · Answer

The Pipes you are talking about in the starting description are different from the pipe you showed in the example.

In Angular(2|4|5) Pipes are used to format view as you said. I think you have a basic understanding of pipes in Angular, you can learn more about that from this link - Angular Pipe Doc

The pipe() you have shown in the example is the pipe() method of RxJS 5.5 (RxJS is the default for all Angular apps). In Angular5 all the RxJS operators can be imported using single import and they are now combined using the pipe method.

tap() - RxJS tap operator will look at the Observable value and do something with that value. In other words, after a successful API request, the tap() operator will do any function you want it to perform with the response. In the example, it will just log that string.

catchError() - catchError does exactly the same thing but with error response. If you want to throw an error or want to call some function if you get an error, you can do it here. In the example, it will call handleError() and inside that, it will just log that string.

User · Answer

Don t get confused with the concepts of Angular and RxJS  We have pipes concept in Angular and pipe   function in RxJS   1  Pipes in Angular  A pipe takes in data as input and transforms it to the desired output     https   angular io guide pipes  2  pipe   function in RxJS  You can use pipes to link operators together  Pipes let you combine multiple functions into a single function    The pipe   function takes as its arguments the functions you want to combine  and returns a new function that  when executed  runs the composed functions in sequence      https   angular io guide rx-library  search for pipes in this URL  you can find the same   So according to your question  you are referring pipe   function in RxJS

User · Answer

RxJS Operators are functions that build on the observables foundation to enable sophisticated manipulation of collections    For example  RxJS defines operators such as map    filter    concat    and flatMap      You can use pipes to link operators together  Pipes let you combine multiple functions into a single function    The pipe   function takes as its arguments the functions you want to combine  and returns a new function that  when executed  runs the composed functions in sequence

User · Answer

Two very different types of Pipes Angular - Pipes and RxJS - Pipes  Angular-Pipe  A pipe takes in data as input and transforms it to a desired output  In this page  you ll use pipes to transform a component s birthday property into a human-friendly date   import   Component   from   angular core     Component     selector   app-hero-birthday     template    lt p gt The hero s birthday is    birthday   date    lt  p gt      export class HeroBirthdayComponent     birthday   new Date 1988  3  15      April 15  1988     RxJS - Pipe  Observable operators are composed using a pipe method known as Pipeable Operators  Here is an example   import  Observable  range  from  rxjs   import  map  filter  from  rxjs operators    const source   Observable lt number gt    range 0  10    source  pipe      map x   gt  x   2       filter x   gt  x   3     0    subscribe x   gt  console log x      The output for this in the console would be the following   0  6  12  18  For any variable holding an observable  we can use the  pipe   method to pass in one or multiple operator functions that can work on and transform each item in the observable collection    So this example takes each number in the range of 0 to 10  and multiplies it by 2  Then  the filter function to filter the result down to only the odd numbers

User · Answer

You have to look to official ReactiveX documentation   https   github com ReactiveX rxjs blob master doc pipeable-operators md   This is a good article about piping in RxJS  https   blog hackages io rxjs-5-5-piping-all-the-things-9d469d1b3f44   In short  pipe   allows chaining multiple pipeable operators   Starting in version 5 5 RxJS has shipped  pipeable operators  and renamed some operators   do - gt  tap catch - gt  catchError switch - gt  switchAll finally - gt  finalize

[angular] What is pipe() function in Angular

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