Compact object

67.7% acceptance

Mar 2, 2026

227

Given an object or array obj, return a compact object. A compact object is the same as the original object, except with keys containing falsy values removed. This operation applies to the object and any nested objects. Arrays are considered objects where the indices are keys. A value is considered falsy when Boolean(value) returns false. You may assume the obj is the output of JSON.parse. In other words, it is valid JSON.

Solution

TypeScript

Time O(n)

Space O(1)

LeetCode

solution.ts

type JSONValue =
  | null
  | boolean
  | number
  | string
  | JSONValue[]
  | { [key: string]: JSONValue };
type Obj = Record<string, JSONValue> | Array<JSONValue>;

function compactObject(obj: Obj): Obj {
  if (Array.isArray(obj)) {
  return (obj as JSONValue[])
    .filter(Boolean)
    .map((item) =>
    typeof item === "object" && item !== null
      ? compactObject(item as Obj)
      : item,
    ) as JSONValue[];
  }
  const result: Record<string, JSONValue> = {};
  for (const key of Object.keys(obj as Record<string, JSONValue>)) {
  const val = (obj as Record<string, JSONValue>)[key];
  if (val) {
    result[key] =
    typeof val === "object" && val !== null
      ? (compactObject(val as Obj) as JSONValue)
      : val;
  }
  }
  return result;
}