flattenArray.js

/*
  Post With Explanation: https://www.linkedin.com/posts/umairjibran_javassript-activity-7031246560059379712-hPp4
*/

const flattenArray = array => {
  return array.reduce((acc, val) => {
    return Array.isArray(val) 
    ? acc.concat(flattenArray(val))
    : acc.concat(val);
  }, []);
};

const nestedArray = [1, [2, [3, 4], 5]];
const flattenedArray = flattenArray(nestedArray);
console.log(flattenedArray); // [1, 2, 3, 4, 5]