Implement a deepOmit function

May 03, 2024

An omit operation on an object is not formally defined in JavaScript, but in general it is widely understood as the process of removing or filtering out certain values based on a condition.

1. Basic implementation

Implement the deepOmit() utility, that removes specified keys and their corresponding values from an object, including nested objects or arrays. Do not mutate the original input.

import isPojo from './src/utils.js';

function deepOmit(input, keys) {
  if (Object.is(input, null)) {
    return input;
  }

  // arrays
  if (Array.isArray(input)) {
    const outputArr = [];
    input.forEach((item) => {
      outputArr.push(deepOmit(item, keys));
    });
    return outputArr;
  }

  // objects
  if (isPojo(input)) {
    const resultObj = Object.create({});
    for (const key in input) {
      if (Object.hasOwn(input, key)) {
        const value = input[key];

        const isExcludedKey = keys.includes(key);

        if (!isExcludedKey) {
          if (typeof value !== 'object') {
            resultObj[key] = value;
          } else {
            resultObj[key] = deepOmit(value, keys);
          }
        }
      }
    }

    return resultObj;
  }

  return input;
}

// Usage
const input = {
  a: 1,
  b: 2,
  c: {
    d: 4,
    e: 5,
    f: [7, 8, { g: 9, i: 10 }]
  },
  h: [1, 2, 3]
};

const output = deepOmit(input, ['d', 'g', 'h']);

/** Yields:
 * {
    "a": 1,
    "b": 2,
    "c": {
        "e": 5,
        "f": [7, 8, { "i": 10 }]
    }
}
*/
console.log(output);

In the above implementation , I have used a utility called isPojo(), which essentially checks if the given value is a Plain Old JavaScript Object or not. You can learn more about it’s implementation in the deepEqual function implementation from the Recursion Questions for Frontend Interviews blog series.