Flat an Array

flatArray.js

// The nested array
const nested =  [[1,2,[3,[8,10]]],4];
// An array that will contain the flatten array
const flat = [];
// The function that runs through the array and flattens it
const scan = (el, arr) =>{
  if(!Array.isArray(el))
    throw "The first parameter should be an array";
  if(!Array.isArray(arr))
    throw "The second parameter should be an array";
  // loops through the nested array
  el.forEach(e => {
    // If the current element is also an array then the scan method is called again
    if(Array.isArray(e))
      scan(e, arr);
    else // if it's not an array it gets inserted into the flat array
      arr.push(e);
  });
}

// run the scan function described above
scan(nested, flat);
// print the flat array
console.log(flat);