wrong solution, this code would return False for a string "a a a aa dab wd qwudbhq wkjdb jkqwdbkdb 948djq9w84 d9*b84wqjd1b89 q4wkj89db jk8qwdj k8qwbd 8kj5qwbd8 q1wb9jkd 2q5w9jkdb 1qwjb8d 1469b19 89589" which is valid by description, because final string is shorter than 140 chars

not working:

let obj = {};
namespace(obj, 'first.second', 5);
namespace(obj, 'first.second');
//undefined

I am afraid your test cases are not ok. Returning values are not correct for some cases and we cannot even console.log for finding why.

Expected: '[70001, 70009, 70061, 70079, 70121, 70141, 70163, 70241]', instead got: '[70001, 70009, 70061, 70079, 70121, 70141, 70163, 70207, 70241]'
Expected: '[70489, 70529, 70573, 70589]', instead got: '[70489, 70507, 70529, 70573, 70589]'

both my returns were correct, pls fix your test cases