Issue with Angular 2 pipe causing unexpected undefined result

Question

Issue with Angular 2 pipe causing unexpected undefined result

Here is a JSON format that I am working with:

[{
  "id": 9156,
  "slug": "chicken-seekh-wrap",
  "type": "dish",
  "title": "Chicken Seekh Wrap",
  "cuisine_type": [2140]
},
{
  "id": 9150,
  "slug": "green-salad",
  "type": "dish",
  "title": "Green Salad",
  "cuisine_type": [2141]
}]

In my Angular2 project, I have created a pipe for filtering by cuisine type:

@Pipe({
      name: 'filter',
      pure: false
 })
 export class FilterPipe implements PipeTransform {
     transform(list: Array<any>, searchTerm: any): Array<any> {
        if(!searchTerm) return list;
        else {
           return list.filter(item => item.cuisine_type[0] == searchTerm);
        } 
     }
 }

I have implemented the pipe in my view like this:

<li *ngFor="let dish of dishes | filter : 2140">
      <h2>{{dish.title}}</h2>
      <input type="checkbox" [formControlName]="dish.id" />
 </li>

However, I encountered the following errors:

ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'filter' of undefined
TypeError: Cannot read property 'filter' of undefined
    at FilterPipe.transform (filter.ts:20)
    at checkAndUpdatePureExpressionInline (core.es5.js:11241)
    at checkAndUpdateNodeInline (core.es5.js:12096)
    at checkAndUpdateNode (core.es5.js:12058)
    at debugCheckAndUpdateNode (core.es5.js:12687)
    at debugCheckDirectivesFn (core.es5.js:12628)
    at Object.View_FourthStepPage_1.currVal_0 [as updateDirectives] (FourthStepPage.html:26)

I would appreciate any help or guidance on what I might be doing wrong. Thank you.

javascript angular typescript

Answer 1

Answer №1

To start, make sure to eliminate the unnecessary ')' at the end of your *ngFor loop. Next, the error is occurring because you are passing null to your filter function. When the filter tries to operate on null, it causes an error since you cannot filter null values. I recommend adding a validation check to ensure that the value being passed is valid. You can update your pipe like this:

@Pipe({
      name: 'filter',
      pure: false
 })
 export class FilterPipe implements PipeTransform {
     transform(list: Array<any>, searchTerm: any): Array<any> {
        if(!list)
          return [];
        if(!searchTerm) return list;
        else {
           return list.filter(item => item.cuisine_type[0] == searchTerm);
        } 
     }
 }

By doing this, you prevent filtering undefined values.

P.S If your data is fetched from a remote server and dishes are stored as observables, you will also need to use the async pipe.

Answer 2

To start, make sure to eliminate the unnecessary ')' at the end of your *ngFor loop. Next, the error is occurring because you are passing null to your filter function. When the filter tries to operate on null, it causes an error since you cannot filter null values. I recommend adding a validation check to ensure that the value being passed is valid. You can update your pipe like this:

@Pipe({
      name: 'filter',
      pure: false
 })
 export class FilterPipe implements PipeTransform {
     transform(list: Array<any>, searchTerm: any): Array<any> {
        if(!list)
          return [];
        if(!searchTerm) return list;
        else {
           return list.filter(item => item.cuisine_type[0] == searchTerm);
        } 
     }
 }

By doing this, you prevent filtering undefined values.

P.S If your data is fetched from a remote server and dishes are stored as observables, you will also need to use the async pipe.

Answer 3

Answer №2

If you are receiving data from a backend source, it's possible that the list has not been fetched yet and your variable is currently undefined. In this situation, there are two recommended solutions to consider.

Approach 1

Instead of verifying the list within your pipe function, it's best practice to avoid this method as it goes against good software practices. Placing additional logic in the pipe can lead to functions becoming overly complex and difficult to maintain.

Best Practice Tip:

The responsibility of the pipe should solely focus on transforming the data without any additional checks or validations. Following the Single Responsibility Principle (SRP) helps in creating cleaner and more efficient codebase.

A preferable approach would be to sanitize the data before transformation by initializing the list with an empty array [].

Approach 2

To ensure smooth functioning, either have the list start off as empty or prevent the *ngFor directive from executing initially. This can be achieved by using *ngIf to hide the element until the data is ready to be displayed.

Answer 4

If you are receiving data from a backend source, it's possible that the list has not been fetched yet and your variable is currently undefined. In this situation, there are two recommended solutions to consider.

Approach 1

Instead of verifying the list within your pipe function, it's best practice to avoid this method as it goes against good software practices. Placing additional logic in the pipe can lead to functions becoming overly complex and difficult to maintain.

Best Practice Tip:

The responsibility of the pipe should solely focus on transforming the data without any additional checks or validations. Following the Single Responsibility Principle (SRP) helps in creating cleaner and more efficient codebase.

A preferable approach would be to sanitize the data before transformation by initializing the list with an empty array [].

Approach 2

To ensure smooth functioning, either have the list start off as empty or prevent the *ngFor directive from executing initially. This can be achieved by using *ngIf to hide the element until the data is ready to be displayed.

Answer 5

Answer №3

This syntax is unfamiliar to me... You may want to attempt the following:

<ul *ngFor="let item of items | filter : 2140">

Answer 6

This syntax is unfamiliar to me... You may want to attempt the following:

<ul *ngFor="let item of items | filter : 2140">

Answer 7

Answer №4

There seems to be an additional ")" in this code snippet after 2140

*ngFor="let dish of dishes | filter : 2140)"

. Simply remove it and give it a try, I have personally tested this fix and can confirm that it works as intended.

Answer 8

There seems to be an additional ")" in this code snippet after 2140

*ngFor="let dish of dishes | filter : 2140)"

. Simply remove it and give it a try, I have personally tested this fix and can confirm that it works as intended.

Issue with Angular 2 pipe causing unexpected undefined result

Answer №1

Answer №2

Approach 1

Approach 2

Answer №3

Answer №4

Similar questions

What is the best way to organize code into separate files while utilizing a module that needs to be included in every file?

The functionality of AJAX is hindered in the browser when attempting to fetch data from a URL

What is the proper way to include jQuery script in HTML document?

Creating dynamic keys using Typescript and JSON data format

Executing a NestJs cron job at precise intervals three times each day: a guide

How can I retrieve the length of an array in vuejs?

Tips on how to retrieve the current value of a scope variable in jQuery

Add() function is not duplicating the formatting

Replicate the ctrl+/- function through coding

Error: The `Field` component encountered a failed prop type validation due to an invalid prop `component` after upgrading to MUI version

Form control identifier and input field name

Can the ajaxsetup error handler be used with the POST method?

Implementing hashing with resumable.js

Using jQuery or JavaScript to clear multiple selections in a multiselect dropdown when a button is clicked

Angular 14 Custom Validator Assistance

the deactivation of my rollover class is being caused by my float class

Executing an npm task from a JavaScript file in a parent/child process scenario

To utilize the span and input text increment functionality, simply use the required input type number and hold either the up or down arrow

Angular service providing a subset of resource data

Is there a way to identify modifications in an Object and an Array when utilized as Input attributes in a sub-component?