Flatten a nested array using .reduce method in Javascript

const arr = [[1],[2],[3],[[4,5],[6,7],[[8,9],[10,11],[12,13]]]];
const initialValue = [];
const flatten = (arr) => arr.reduce((flattened,toFlatten) => {
  return flattened.concat(Array.isArray(toFlatten) ? flatten(toFlatten): toFlatten);    
}, []); 
console.log(flatten(arr));

This is a very interesting one liner to flatten an array. We’re using reduce method on the array and inside the reducer function, we check if the toFlatten argument is an array or not. If not, then we call the function recursively.

array, javascript, node, tech, technology — Jan 1, 2022