Flatten a javascript array

flattenArray.js

var arr1 = ['a', 'b', 'c'];
console.log(arr1.length);
var arr2 = ['d', 'e', 'f'];
console.log(arr2.length);
var arr3 = ['g', 'h', 'i'];
console.log(arr3.length);
var nested = [arr1, arr2, arr3];
console.log('nested=' + nested);
console.log(nested.length);
var flattened = [].concat.apply([], nested);
console.log('resut=' + flattened);
console.log(flattened.length);