This is a custom method to partition any array based on the logic provided

partition.js

/**
 * A function that partitions an array based on the passed logic
 * @param arr The array to be partitioned
 * @param callback The logic function to base the partition on
 */
const partition = (arr, callback) => {
  // The result object which will ultimately have two properties
  // positive and negative
  const result = {};
  arr.forEach((item, index) => {
    // Here the callback will return either positive or negative string
    const key = callback(item, index);
    
    // If any key is coming for the first time
    if(!result.hasOwnProperty(key)) {
      result[key] = [];
    }
    result[key].push(item);
  })
  //result will have {"positive": [1, 3, 5], "negative": [-4, -2, -6]}
  return result;
}

// The array to be partitioned
const arr = [1, 3, -4, 5, -2, -6];

//partition function in action
const {positive, negative} = partition(arr, (item, index) => {
  return item > 0 ? "positive" : "negative";
});

console.log(positive);
// [1, 3, 5]
console.log(negative);
// [-4, -2, -6]