Codewars 7 kyu Square Every Digit Javascript

this one we use the split(), map(), and join() methods with more stuff split() info: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split map() info: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map join() info: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join Number() constructor info: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/Number String() constructor info: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/String unary plus(+) info: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Unary_plus