Use match in conjunction with a global flag, instead of split. {1,6} is needed, to also include the last part of the matched string. Patterns are greedy by default, which means that as much is matched as possible. So, .{1,6} will only match less than 6 characters at the end of a string.

'abcdefghijklmnopqrstuvwxyz'.match(/.{1,6}/g);

Result:

[abcdef, ghijkl, mnopqr, stuvwx, yz];

_{Note that the returned object is a true array. To verify:}

console.log('.'.match(/./g) instanceof Array);  //true