Angular 2's filter pipe is not producing any results

Question

Angular 2's filter pipe is not producing any results

I am facing an issue with using the filter pipe to filter my data as it is returning an empty page. Interestingly, when I remove the | filter from the HTML code, the data appears as expected. The filter pipe should display all names if the name exists.

This is my first time working with the filter pipe, so please let me know if there are any mistakes in the implementation.

Data Sample

[

    {
        "name": "Alien",
        "age": 18,
        "address": "lorem ipsum"
    },
    
    {
        "name": "Peter",
        "age": 17, 
        "address": "lorem ipsum"
    },
    
    {
        "name": "Ben",
        "age": 20, 
        "address": "lorem ipsum"
    }

HTML Code

<ion-item *ngFor="let list of this.data | filter: 'name'">
  
  <h2>{{ list.name }}</h2>
  
</ion-item>

Filter Pipe Logic

export class MyPipe implements PipeTransform {

transform(listArray: any, value: any): any {

if (value === undefined) return listArray;

for (let i = 0; i < listArray.length; i++) {
  
  if (listArray[i].indexOf(value) !== -1) {
      return value;
  }
  
}

}
  
}

angular typescript angular2-pipe

Answer 1

Answer №1

When you write

listArray.indexOf("value")

The method will return the items that have exactly the string "value" inside the array.

I believe what you intended to use is

listArray.indexOf(value)

Answer 2

When you write

listArray.indexOf("value")

The method will return the items that have exactly the string "value" inside the array.

I believe what you intended to use is

listArray.indexOf(value)

Answer 3

Answer №2

Before using your pipe, make sure to give it a name and use the 'value' attribute instead of just typing out 'value' as a string.

@Pipe({ name: 'customFilter' })
export class FilterPipe implements PipeTransform {
transform(inputArray: any[], searchValue: any): any[] {
if (searchValue === undefined) return inputArray;
for (let i = 0; i < inputArray.length; i++) {
if (inputArray.indexOf(searchValue)) {
return searchValue;
}
}
}
}

Answer 4

Before using your pipe, make sure to give it a name and use the 'value' attribute instead of just typing out 'value' as a string.

@Pipe({ name: 'customFilter' })
export class FilterPipe implements PipeTransform {
transform(inputArray: any[], searchValue: any): any[] {
if (searchValue === undefined) return inputArray;
for (let i = 0; i < inputArray.length; i++) {
if (inputArray.indexOf(searchValue)) {
return searchValue;
}
}
}
}

Answer 5

Answer №3

Here is how I approached the task:

filter.pipe.ts

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

@Pipe({
  name: 'filter'
})

export class FilterPipe implements PipeTransform {

  /**
   * The value parameter represents an array of servers
   */
  transform(value: any, filterString: string, propName: string): any {
    if(value.length === 0) {
      return value;
    }

    const resultArray = [];

    // Iterating through the items in the value array
    for(const item of value) {
      // Checking if the server status matches the filter criteria
      if(item[propName] === filterString) {
        resultArray.push(item);
      }
    }
    return resultArray;
  }
}

app.component.html

<div class="container">
  <div class="row">
    <div class="col-xs-12 col-sm-10 col-md-8 col-sm-offset-1 col-md-offset-2">
      <input type="text" [(ngModel)]="filteredStatus" class="form-control" placeholder="Filter by status">
      <hr>
      <ul class="list-group">
        <li
          class="list-group-item"
          *ngFor="let server of servers | filter: filteredStatus: 'status'"
          [ngClass]="getStatusClasses(server)">
          <span
            class="badge">
            {{ server.status }}
          </span>
          <strong>{{ server.name | shorten: 15 }}</strong> |
          {{ server.instanceType | uppercase }} |
          {{ server.started | date:'fullDate' | uppercase }}
        </li>
      </ul>
    </div>
  </div>
</div>

app.component.ts

  filteredStatus = '';

  appStatus = new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve('stable');
    }, 2000);
  });

  servers = [
    {
      instanceType: 'medium',
      name: 'Production',
      status: 'stable',
      started: new Date(15, 1, 2017)
    },
    {
      instanceType: 'large',
      name: 'User Database',
      status: 'stable',
      started: new Date(15, 1, 2017)
    },
    {
      instanceType: 'small',
      name: 'Development Server',
      status: 'offline',
      started: new Date(15, 1, 2017)
    },
    {
      instanceType: 'small',
      name: 'Testing Environment Server',
      status: 'stable',
      started: new Date(15, 1, 2017)
    }
  ];

Answer 6

Here is how I approached the task:

filter.pipe.ts

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

@Pipe({
  name: 'filter'
})

export class FilterPipe implements PipeTransform {

  /**
   * The value parameter represents an array of servers
   */
  transform(value: any, filterString: string, propName: string): any {
    if(value.length === 0) {
      return value;
    }

    const resultArray = [];

    // Iterating through the items in the value array
    for(const item of value) {
      // Checking if the server status matches the filter criteria
      if(item[propName] === filterString) {
        resultArray.push(item);
      }
    }
    return resultArray;
  }
}

app.component.html

<div class="container">
  <div class="row">
    <div class="col-xs-12 col-sm-10 col-md-8 col-sm-offset-1 col-md-offset-2">
      <input type="text" [(ngModel)]="filteredStatus" class="form-control" placeholder="Filter by status">
      <hr>
      <ul class="list-group">
        <li
          class="list-group-item"
          *ngFor="let server of servers | filter: filteredStatus: 'status'"
          [ngClass]="getStatusClasses(server)">
          <span
            class="badge">
            {{ server.status }}
          </span>
          <strong>{{ server.name | shorten: 15 }}</strong> |
          {{ server.instanceType | uppercase }} |
          {{ server.started | date:'fullDate' | uppercase }}
        </li>
      </ul>
    </div>
  </div>
</div>

app.component.ts

  filteredStatus = '';

  appStatus = new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve('stable');
    }, 2000);
  });

  servers = [
    {
      instanceType: 'medium',
      name: 'Production',
      status: 'stable',
      started: new Date(15, 1, 2017)
    },
    {
      instanceType: 'large',
      name: 'User Database',
      status: 'stable',
      started: new Date(15, 1, 2017)
    },
    {
      instanceType: 'small',
      name: 'Development Server',
      status: 'offline',
      started: new Date(15, 1, 2017)
    },
    {
      instanceType: 'small',
      name: 'Testing Environment Server',
      status: 'stable',
      started: new Date(15, 1, 2017)
    }
  ];

Angular 2's filter pipe is not producing any results

Answer №1

Answer №2

Answer №3

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