Why does the If condition in the recursion return undefined?

Question

JavaScript

Checked the ELSE thread. Everything works correctly there. When the isHappy(1) function is called, undefined is returned instead of true.

var isHappy = function(n) {
    if (n === 1) return true 
    else if (n != 1 && n < 10) return false 
    else {
        const array = Array.from(`${n}`);
        const output = array.map(num =>num * num).reduce((acc, curr) => acc + curr);
        isHappy(output);
    }
};

console.log(isHappy(19))

Answer 1

Because to return something, you need to use return.