Trying to write a inverse version of Javascript's filter method that will work on both arrays and objects

So as the question states, I'm attempting to write a function for which the input can be either an Array or an Object (as well as a callback to test them against).

The desired return value is an Array / Object of the elements (value/key pairs in the case of the Object) that passed the test - but the original Array / Object should be updated to remove those elements.

For example - if you passed in an "isEven" callback function that determines if numbers are even, then the expected results would be:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let a = [1, 2, 3, 4]
reject(a)

//Output:
[2, 4]


console.log(a);
//expected output
[1, 3]

<!-- end snippet -->

So far I've been trying to write an conditional scenario based on Array.isArray(input), to use one set of code for handling arrays, another set for handling objects. However, it's been not working properly for objects, and I'm curious if there'd be one way to write it that would work for both cases? If not what might be the best approach here?

My rough attempt to this point, if the code is helpful:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

function reject(collection, callback) {
  let newArr;
  if (!collection.constructor == Array) {
    newArr = {};
    for (let [key, value] of Object.entries(collection)) {
      if (!callback(value)) {
        newArr[key] = value;
      }
    }
  } else {
    newArr = [];
    for (let el of collection) {
      if (!callback(el)){
        newArr.push(el);
      }
    }
  }
  return newArr;
}

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You can use Array.isArray to check if an object is an array. To remove elements from the array, you can iterate backwards and use Array#splice.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

function reject(o, f) {
  if (Array.isArray(o)) {
    let res = [];
    for (let i = o.length - 1; i >= 0; i--)
      if (f(o[i])) res.push(o.splice(i, 1)[0]);
    return res.reverse();
  }
  let res = {};
  for (const [k, v] of Object.entries(o)) 
    if (f(v)) {
      res[k] = v;
      delete o[k];
    }
  return res;
}
let a = [1, 2, 3, 4];
console.log(reject(a, x => x % 2 === 0), a);
let obj = {a : 1, b : 2, c : 3, d : 4};
console.log(reject(obj, x => x > 2), obj);

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