Nsryjdtyk

I have tried using custom pipe.This is my pipe file

import { Pipe, PipeTransform } from '@angular/core';

import { User } from 'src/app/user';

import { ApiService } from 'src/app/api.service';

import { Observable } from 'rxjs';

import { isNgTemplate } from '@angular/compiler';

import { map } from 'rxjs/operators';



@Pipe({

  name: 'my-pipe'



})

export class MyPipePipe implements PipeTransform {

  isEqual = false;

  api: ApiService;



  transform(post_id: number, users: Observable< User> ): any {

   // users = this.api.getUserList();

    users.subscribe(user => user.filter(userss => {

      if (userss.id === post_id && post_id !== null) { this.isEqual = true; } else {

        console.log(this.isEqual + ' ' + ' hataa');

      }

    }));



  }

All i want is nonexistent users cant post.Therefore i trying user's id equalize with post's userId.Here is my html code

    <div class="form-group">

      <label for="userId">User Id</label>

      <input type="number" class="form-control" id ="userId" name="userId" required [(ngModel)]="posts.userId">

     <!--<div   class="tetx text-danger" *ngIf="!isEqual" >Invalid Id!!!</div>--> 

      <div  *ngIf=" my-pipe: posts.userId " >



Invalidd





      </div>



    </div>

But unfortunately I get this error:

[Angular] TypeError: Cannot read property 'toUpperCase' of undefined

The error comes from Angular compiler that tries to compile your template.

Choose another name for your pipe, i.e. myPipe:

@Pipe({

  name: 'myPipe'

...

*ngFor="let u of users_s | myPipe"

And you can't use pipe without passing value to it:

*ngIf=" my-pipe: posts.userId "

it should be something:

*ngIf="postId | myPipe"