var arr1 = [[0, 1], [2, 3], [4, 5]];
var arr2 = arr1.reduce(function (a, b) { return a.concat(b)} );
// arr2 [0, 1, 2, 3, 4, 5]
var arr1 = [[0, 1], [2, 3], [4, 5]];
function flatten(arr) { return [].concat( ...arr.map(x => Array.isArray(x) ? flatten(x) : x) ) }
var arr2 = flatten(arr1); // arr2 [0, 1, 2, 3, 4, 5]
优点: 多维数组也可以
比如:var arr = [[1,2],3,[[[4], 5]]]