Array flat (Infinity) is flattened to achieve deep parsing of multidimensional arrays into a new array

①

var arr1 = [1, 2, [3, 4]];
arr1.flat(); 
//输出为： [1, 2, 3, 4]

②

var arr2 = [1, 2, [3, 4, [5, 6]]];
arr2.flat();
//输出为： [1, 2, 3, 4, [5, 6]]

③

var arr3 = [1, 2, [3, 4, [5, 6]]];
arr3.flat(2);
//输出为： [1, 2, 3, 4, 5, 6]

④ (Use Infinity as the depth to expand nested arrays of any depth)

arr4.flat(Infinity); 
//输出为： [1, 2, 3, 4, 5, 6]

⑤ ( flat() method will remove empty items in the array )

var arr5 = [1, 2, , 4, 5];
arr5.flat();
//输出为： [1, 2, 4, 5]