Error message encountered following the removal of an undesirable type from an array in Typescript

When working with TypeScript, I am facing an issue. I have an array defined as Array<string|undefined, and my goal is to filter out the undefined values from this array and assign the resulting array to a variable of type Array<string>. However, I am encountering a type error. How can I solve this problem?

For example:

const a: Array<string|undefined> = ['a', undefined, 'b'];
const b: Array<string> = a.filter(Boolean); // ERROR

The error message states:

Type 'string | undefined' is not assignable to type 'string'. Type 'undefined' is not assignable to type 'string'.

typescript

Answer №1

let array: Array<string|undefined> = ['apple', undefined, 'banana'];

let filteredArray: Array<string> = array.filter(element => element);

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