Quick 'n dirty JavaScript interview question #1

flatten-array.js

/**
 *  Given an array of n length, where each item in the array may be a letter,
 *  number or another array, write a function that will return a flattened
 *  array containing all the values in the original array and its children.
 * 
 * Ex.
 * 
 * var arr = [ 1, 'b', [ 'c', [ 4 ], 5], 'f'];
 * flatten(arr) === [1, 'b', 'c', 4, 5, 'f'];
 */
var arr = [ 1, 'b', [ 'c', [ 4 ], 5], 'f'];

function flatten(arr) {
  
  var result = []
    , i = 0
    , len = arr.length;
  
  for (i; i < len; i++) {
    
    // Using instanceof because typeof will always return 'object', 'string', 'number' or 'undefined'
    if (arr[i] instanceof Array) {
      
      // Using recursion to account for n-dimensions
      result = result.concat(flatten(arr[i]));
    }
    else {
      result.push(arr[i]);
    }
  }
  
  return result;
}