Tips for fixing: "Object may be null" error in Angular routing

Currently, I am working on the angular heroes tutorial provided in the angular documentation and encountering an error.

An issue has been detected, which states that the object is possibly 'null'.

getHero(): void {
const id = +this.route.snapshot.paramMap.get('id');
this.heroService.getHero(id)
  .subscribe(hero => this.hero = hero);

}

This is located in the hero-detail.component.ts file.

If you would like to view the full code snippet, please follow this link to the hero-detail component.

I have come across suggestions advising to set it to false in the config.json, but I am seeking assistance on how to resolve this without simply suppressing the issue.

Thank you in advance for your help.

angulartypescriptangular-routing

Answer №1

Completing this task is simple with just two steps

fetchCharacter(): void {
  const param=this.route.snapshot.paramMap.get('id');
  const id = param?+param:0;
  this.characterService.fetchCharacter(id)
    .subscribe(character => this.hero = character);
}

Answer №2

The reason for this issue is the stray plus sign combined with the possibility that the item 

this.route.snapshot.paramMap.get('id')
could be null according to the Typescript type system, making it an invalid operand for +.

I replicated the same error with this code on this playground

const thing:string|null;

function getHero() : void {
const id = +thing;
}

Pay attention to the line...

const id = +thing;

https://i.sstatic.net/ijPXs.png

If you intended to use the + as Elisio suggested in the comment below, then you must add a condition to prevent getHero from executing when id is null or ensure a reliable substitute value is provided before execution. As long as there's a chance of it being null,

Typescript cannot ensure the operation's success. This serves as a reminder to perform checks and include safety measures.

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