Creates a new javascript object from bigger javascript object by taking certain properties from it.

Object.extract.js

/*
 * Creates a new javascript object from bigger javascript object by taking certain properties from it.
 *
 * @param {object} input - Main javascript object
 * @param {array} keys - Keys that will be used to create a new object.
 */

Object.prototype.extract = function extract(input, keys) {
  return Object.prototype.toString.call(input) === '[object Object]'
    ? Object.keys(input)
        .filter(
          k =>
            Array.isArray(keys)
              ? keys.indexOf(k) !== -1
              : typeof keys == 'string'
                ? [keys].indexOf(k) !== -1
                : typeof keys == 'number'
                  ? [String(keys)].indexOf(k) !== -1
                  : false
        )
        .reduce((memo, key) => {
          memo[key] = input[key]
          return memo
        }, {})
    : {}
}

// Test Cases
const obj1 = {
  a: 'A',
  b: 'B',
  c: 'C',
  d: 'D',
  8: 'Eight',
  0: 'Zero'
}

obj1.extract(obj1, ['a', 'd']) === { a: 'A', d: 'D' }
obj1.extract(obj1, ['t']) === {}
obj1.extract(obj1, '8') === { '8': 'Eight' }
obj1.extract(obj1, 8) === { '8': 'Eight' }
obj1.extract(undefined) === {}
obj1.extract() === {}