Is it possible to remove undefined from an array in a TypeScript will recognize?

Question

Is there a clean and convenient way to do something like:

const x: (string|undefined)[] = ['aaa', undefined, 'ccc'];
const y = _.filter(x, it => !!it);

so that TypeScript recognizes the type of y as string[], without having to write my own function doing the filtering? (I.e. is there a way to have the language feature that narrows the type of a variable in say an if block apply to arrays?)

Patrick Roberts · Accepted Answer · 2019-03-04 02:50:29Z

5

Not sure why you need lodash here but yes:

const x: (string|undefined)[] = ['aaa', undefined, 'ccc'];
const y = x.filter((it): it is string => it !== undefined);

In this case, y is inferred as type string[]. The !!it would also be inferred as type string[], but has the side-effect of also filtering out empty string entries from the array.

edited Mar 4, 2019 at 2:50

answered Mar 4, 2019 at 2:44

Patrick Roberts

52.4k10 gold badges120 silver badges166 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Is it possible to remove undefined from an array in a TypeScript will recognize?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related