CODEWITHSUNDEEP
typescript
SimpleJ
SimpleJ

Reputation: 14768

Destructuring an array is removing the possible undefined value from the type

Is there any way to get typescript to not ignore the possibility that an array could be empty when destructuring? For example in this snippet

const numbers: number[] = [];
const [n] = numbers;

type T = typeof n;

The type T evaluates to number, but it should evaluate to number | undefined since the value of n is undefined.

Upvotes: 1

Views: 98

Answers (1)

Bhargav Shah
Bhargav Shah

Reputation: 865

type Tnumber = number | undefined;
const numbers: Tnumber[] = [];
const [n] = numbers;

type T = typeof n;

const one: T = undefined;
const two: T = 5;

Create a new type Tnumber. Later on you the inferred type T can be either number or undefined.

Interestingly, typeof n is undefined. From this behaviour it looks like the Typescript compiler infers the type of the destructured value from the original type of the array, rather than it's current value.

Upvotes: 1

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