How to transform a string of this format '[11, 66]' to an array ? 
Array.isArray('[11, 66]') return false since it's considered as string?
A good way to do this would be JSON.parse.
The JSON.parse() method parses a JSON string, constructing the JavaScript value or object described by the string.
In your example:
JSON.parse('[11, 66]')
Output:
[11, 66]
11and66(hint: it is valid JSON) ?'[1, 2]'.substring(1, s.length - 1).split(', ').map(str => +str)also works, but is less robust thanJSON.parse.