@d-healey Ok you are right, it doesn't have directly an id field. Woocommerce user retrieve response is in an array format. So:
var usid = response[0].id; works.
[ { "id": 12345, "date_created": "", "date_created_gmt": "", "date_modified": "", "date_modified_gmt": "", "email": "USER_EMAIL", "first_name": "", "last_name": "", "role": "customer", "username": "", "billing": { "first_name": "", "last_name": "", "company": "", "address_1": "", "address_2": "", "city": "", "postcode": "", "country": "", "state": "", "email": "", "phone": "" }, "shipping": { "first_name": "", "last_name": "", "company": "", "address_1": "", "address_2": "", "city": "", "postcode": "", "country": "", "state": "" }, "is_paying_customer": true, "avatar_url": "", "meta_data": [ { "id": , "key": "", "value": "" }, { "id": , "key": "", "value": "" } ], "_links": { "self": [ { "href": "" } ], "collection": [ { "href": "" } ] } } ]