JavaScript recursive function using ternary operator

Question

why is it necessary to add return statement before ternary operator in recursive function to return function output?

// This dose not work

    function rec(n) {
      n == 1 ? n : n + rec(n - 1);
    }

// This works as return statement is added before ternary operator
    function rec(n) {
      return n == 1 ? n : n + rec(n - 1);
    }

// This works
    function rec(n) {
      if (n == 1) return 1;
      return n + rec(n - 1);
    }

Answer 1

// If you would like to do this in one line then correct solution would be:
    let rec = n => n == 1 ? n : n + rec(n - 1);
// Now you dont need to add the return keyword before

// This works as return statement is added before ternary operator
    function rec(n) {
      return n == 1 ? n : n + rec(n - 1);
    }

// This works
    function rec(n) {
      if (n == 1) return 1;
      return n + rec(n - 1);
    }