Write a function to flatten an array in JavaScript.

Question

Anonymous · Accepted Answer

function flatten(array) {
  array.reduce(function(flat, toFlatten) {
    return flat.concat(Array.isArray(toFlatten) ? flatten(toFlatten) : toFlatten); 
  }, []);
}

Dennis Vash · Answer

// flat deep recursion
const flatArr = arr =>
  arr.reduce(
    (acc, val) => acc.concat(Array.isArray(val) ? flatArr(val) : val),
    []
  );

// flat deep no recursion
const flatDeep = input => {
  const stack = [...input];
  const res = [];

  while (stack.length) {
    const currValue = stack.pop();

    Array.isArray(currValue) ? stack.push(...currValue) : res.push(currValue);
  }

  return res.reverse();
};

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