TypeScript · question
Q.13 of 99
What is `NonNullable<T>` utility type?
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Re-explain
NonNullable<T> removes null and undefined from a type:
type MaybeString = string | null | undefined;
type DefinitelyString = NonNullable<MaybeString>; // string
function processValue(value: string | null | undefined): void {
if (value !== null && value !== undefined) {
// Type narrowing
const processed: NonNullable<typeof value> = value; // string
console.log(processed.toUpperCase());
}
}
// Useful with arrays
type ArrayItem<T> = T extends (infer U)[] ? NonNullable<U> : never;
type StringArrayItem = ArrayItem<(string | null)[]>; // string
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