javascript + nested array into single array code example

Example 1: array flatten

const arr = [1, 2, [3, 4]];

// To flat single level array
arr.flat();
// is equivalent to
arr.reduce((acc, val) => acc.concat(val), []);
// [1, 2, 3, 4]

// or with decomposition syntax
const flattened = arr => [].concat(...arr);

Example 2: flatten an array in javascript

// Although this now may be an older version of how to faltten an 
// array of arrays. I still want to post it so some may have an understanding 
// of how it works

function falltenArray(arr) {
  
  let result = [...arr];
  let flattened = false;
  let counter = 0;
  
  while (flattened === false){
	// checks to see if the element at the counter index is an array
      if (Array.isArray(result[counter])){
        // unpacks the current array element back into the array
        result.splice(counter, 1, ...result[counter]);
        // if so the counter should start at the beginning of the array
        counter = 0;
        
      } else {
        counter += 1;
      }

      if (counter === result.length){
        flattened = true;
      }
  }
  
  return result;
}