Implement 'filter' with reduce.

filterwithreduce.js

// Credit: Tweet from @oliverjumpertz: https://twitter.com/oliverjumpertz/status/1460184236917460993

// Filtering means: Test all elements of an array and take those with you that succeed the test
const filter = (array, callback) =>   array.reduce((accumulator, current, index, arr) => {
    // This is the filter function. It decides which element is added to the new array
    if (callback(current, index, arr)) {
      // For each iteration, the current element is tested with the callback. If that test succeds
      // it's added to the resulting array.
      accumulator.push(current);
    }
    return accumulator;
    // You want a new array as the initial value
  }, []);