About typescript define an object who has not contain a field the type defined-CodePudding

Assume I have an interface Book:

interface Book {
    id: number
    info: {
        name: string,
    }
}

Now I define a list named bookList:

const bookList: Book[] = [
    {
        id: 1,
        info: {
            name: 'bookA',
        }
    },
    {
        id: 2
    }
]

Absolutely I will get an error like this:

Property 'info' is missing in type '{ id: number; }' but required in type 'Book'.

Then I add a ? to the Book like this:

interface Book {
    id: number
    info?: {
        name: string,
    }
}

The error will gone.

But when I get name like below:

console.log('book name', bookList[0].info.name)

Here comes another error:

Object is possibly 'undefined'.

Of cause I can do like this: bookList[0].info!.name or bookList[0].info?.name But I have multiple code like bookList[0].info.name, I don't want to add ! or ? everywhere.

Could someone please kindly suggest me how to solve this?

Here is the Typescript Playground

CodePudding user response：

That's right becase info property is possibly undefiend you can have question mark by using that, like this :

console.log('book name', bookList[0].info?.name)

CodePudding user response：

One way would be to put ! after info. console.log('book name', bookList[0].info!.name)

Note: ! operator tells the compiler to ignore the possibility of it being undefined.