guest271314 (2019-05-10T14:35:58.000Z)
guest271314 at gmail.com (2019-05-10T14:41:12.568Z)
Still not gathering the significance or purpose of using ```in``` to generate a boolean output. What appears to be the requirement can be achieved by using ```Set``` or ```Map``` ``` let m = new Map([[0, "a"],[ 1, 1], [2, {}]]); m.has(0); // true m.get(2) // {} ```