Remove null attributes from an Object in Typescript

Question

As reference Remove blank attributes from an Object in Javascript, how to make it Typescript compatible?

JS function (nested objects | ES10):

function removeEmpty(obj) {
  return Object.fromEntries(
    Object.entries(obj)
      .filter(([_, v]) => v != null)
      .map(([k, v]) => [k, v === Object(v) ? removeEmpty(v) : v])
  );
}

I've tried with Exclude<T, null> but it doesn't works with nested objects and I think it's not the correct utility to use.

Note that the returned type should remove null type(s) but keeps undefined.

Example/Expected behaviour:

type TestType = {
  a?: {
    b?: {
      c: string;
    } | null;
    z?: {
      x: string;
    };
  } | null;
};

const testObj: TestType = {
  a: {
    b: null,
    z: { x: 'Hi' }
  }
};

const resultObj = removeEmpty(testObj);

Where resultObj type is similar to:

type ResultTestTypeExample = {
  a?: {
    b?: {
      c: string;
    };
    z?: {
      x: string;
    };
  };
};

AxaZol · Accepted Answer · 2025-04-02 09:48:37Z

6

Does this work for you?

type ExpandRecursively<T> = T extends object
  ? T extends infer O ? { [K in keyof O]: ExpandRecursively<O[K]> } : never
  : T;

type RemoveNull<T> = ExpandRecursively<{ [K in keyof T]: Exclude<RemoveNull<T[K]>, null> }>

Usage:

function removeEmpty<T extends object>(obj: T): RemoveNull<T> {
  return Object.fromEntries(
    Object.entries(obj)
      .filter(([_, v]) => v != null)
      .map(([k, v]) => [k, v === Object(v) ? removeEmpty(v) : v])
  ) as RemoveNull<T>
}

Playground

edited Apr 2 at 9:48

AxaZol

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answered May 11, 2022 at 16:12

Tobias S.

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2 Comments

martin8768 Over a year ago

I get this error:

martin8768 Over a year ago

No overload matches this call. Overload 1 of 2, '(o: { [s: string]: unknown; } | ArrayLike<unknown>): [string, unknown][]', gave the following error. Argument of type 'T' is not assignable to parameter of type '{ [s: string]: unknown; } | ArrayLike<unknown>'. Type 'T' is not assignable to type 'ArrayLike<unknown>'. Overload 2 of 2, '(o: {}): [string, any][]', gave the following error. Argument of type 'T' is not assignable to parameter of type '{}'.ts(2769)

AxaZol · Accepted Answer · 2025-03-28 17:17:02Z

0

export function removeNull<T extends object>(obj: T | any) {
  Object.keys(obj).forEach(k => {
    const key = k as keyof T
    if (obj[key] && typeof obj[key] === 'object') removeNull(obj[key])
    else if (obj[key] == null) delete obj[key]
  })
  return obj
}

You can remove null elements with the code above. You can also give your type and it will remove all nested objects properties

edited Mar 28 at 17:17

AxaZol

254 bronze badges

answered Feb 8, 2023 at 10:39

Habibov Ulug'bek

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