Is there an easy way to make nested array flat?

Question

That is to make this:

[ ['dog','cat', ['chicken', 'bear'] ],['mouse','horse'] ]

into:

['dog','cat','chicken','bear','mouse','horse']

Answer 1

var flattened = [[0, 1], [2, 3], [4, 5]].reduce(function(a, b) {
  return a.concat(b);
});
// flattened is [0, 1, 2, 3, 4, 5]

It's note worthy that reduce isn't supported in IE 8 and lower.

developer.mozilla.org reference

Answer 2

In modern browsers you can do this without any external libraries in a few lines:

Array.prototype.flatten = function() {
  return this.reduce(function(prev, cur) {
    var more = [].concat(cur).some(Array.isArray);
    return prev.concat(more ? cur.flatten() : cur);
  },[]);
};

console.log([['dog','cat',['chicken', 'bear']],['mouse','horse']].flatten());
//^ ["dog", "cat", "chicken", "bear", "mouse", "horse"]