Angular template error: Potential is present but not defined

Encountering an issue with my Angular application's template file (dashboard.component.html). The error message reads "Object is possibly 'undefined'." Here's the portion of the template that seems to be causing the problem:

<div>
    <p class="title">Dashboard</p>

    <ul>
       @for(post of posts; track post.title){
        @if(post.id%2==0){
            <li>{{post.id}}-{{post.title}}</li>
        }
       }
    </ul>
</div>
// dashboard.component.ts

import { Component } from '@angular/core';
import { AuthService } from '../auth.service';

@Component({
    selector: 'app-dashboard',
    standalone: true,
    imports: [],
    templateUrl: './dashboard.component.html',
    styleUrl: './dashboard.component.scss',
})

export class DashboardComponent {
    email = localStorage.getItem('email');
    posts:any;
    constructor(private authService: AuthService) { 
        this.GetAllPosts();
    }

    signOut() {
        this.authService.signOut();
    }

    GetAllPosts(){
        this.authService.getAllPosts().subscribe((res)=>{
            this.posts = res;
        })
    }
}

The error specifically points to line 10, where I'm attempting to iterate over posts using an @for loop and checking if post.id % 2 == 0. However, TypeScript is flagging it as a potential error because posts could be undefined or null.

How should I modify this template code to handle the scenario where posts might be undefined without triggering this error?

Answer №1

To ensure the modulus operation works correctly, consider setting the value to zero if it's undefined. In the snippet below, if post?.id is undefined, the || or condition will assign a default value of zero:

<div>
    <p class="title">Dashboard</p>

    <ul>
       @for(post of posts; track post.title){
        @if((post?.id || 0) % 2 === 0){
            <li>{{post.id}}-{{post.title}}</li>
        }
       }
    </ul>
</div>

Answer №2

To ensure posts is not null or undefined, use an If condition before looping through posts

For instance:

<div>
    <p class="title">Dashboard</p>
    @if(posts && posts.length){
        <ul>
            @for(post of posts; track post.title){
                @if(post.id%==2){
                    <li>{{post.id}}-{{post.title}}</li>
                }
            }
        </ul>
    }
</div>

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