Recursion Example

flatten.js

/**
 * A Little example of recursion
 **/

(function(){
  var flatten = function(toFlatten){
    var flatArr = [],
        result,
        tmp;

    if (typeof(toFlatten) !== 'undefined' && toFlatten instanceof Array){
      for(var i = 0; i < toFlatten.length; ++i){
        if(toFlatten[i] instanceof Array){
          tmp = flatArr;
          result = tmp.concat(flatten(toFlatten[i]));
          flatArr = result;
        } else {
          flatArr.push(toFlatten[i]);
          result = flatArr; 
        }
      }
    } else { 
      return null;
    }

    return result;
  }

  console.log( flatten( [1,2,3,4,5,6] ) ); //-> [1, 2, 3, 4, 5, 6]
  console.log( flatten( [1,2,3,4,5,6, [1] ] ) ); //-> [1, 2, 3, 4, 5, 6, 1]
  console.log( flatten( [ {}, [1,2,3,4,5,6] ] ) ); //-> [Object, 1, 2, 3, 4, 5, 6]
  console.log( flatten( [ [1], [1,2,3] ] ) ); //-> [1, 1, 2, 3]
  console.log( flatten( [ [1], [1,2,3], [1] ] ) ); //-> [1, 1, 2, 3, 1]
  console.log( flatten( [ [1,[1,2,3,[1,2,3,[1,2,3]]]], [1,2,3], [1] ] ) ); //-> [1, 1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3, 1]
  console.log( flatten( [ ['a',['b',2,3,['c',2,3,[true,2,3]]]], [1,2,3], [1] ] ) ); //-> ["a", "b", 2, 3, "c", 2, 3, true, 2, 3, 1, 2, 3, 1]
  console.log( flatten( [ ['a',['b',2,3,['c',2,3,[true,2,3]]]], [1,(function(){return false;})(),3], [1] ] ) ); //-> ["a", "b", 2, 3, "c", 2, 3, true, 2, 3, 1, false, 3, 1]
})();

Here is a little example of recursion that I cooked up. It will take an array with N nested arrays and flatten them. The contents of those arrays can be anything. One way to test this code would simply be to copy and paste the code into the Chrome Developer Tools and observe the output :)