I have an array of type X[] | undefined, I want to extract X type from it and use it after.

what I have tried is:

type X = typeof X[number]

but it gives syntax error because of the undefined.

CodePudding user response：

You need to exclude the undefined from the type first. You can use NonNullable:

declare const X: string[] | undefined
type XItem = NonNullable<typeof  X>[number]

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