Is there a way to make sure, that the compiler will cry every time I try to access an array by index?

In my example, I explicitly say, that the record could be undefined, but the compiler still won't cry.

type MyDataType =  { id: number, name: string };

const array: MyDataType[] = [
    { id: 1, name: "Hey folks" },
]

const record: MyDataType | undefined = array[1];

What is the best approach to make it evident, that array[index] can return undefined or maybe even null?

CodePudding user response：

Typescript 4.1 or later

Add noUncheckedIndexedAccess to your compilerOptions in your tsconfig.json file.

// tsconfig.json
{
  "compilerOptions": {
    "noUncheckedIndexedAccess": true
  }
}

Playground

CodePudding user response：

type MyDataType =  { id: number, name: string };

type NullableArray<T> = {
    [K in number]: T | undefined
}

const array: NullableArray<MyDataType> = [
    { id: 1, name: "Hey folks" },
]

const record: MyDataType  = array[1];

Playground