最简单的递归函数返回未定义

Question

Code:

function forLoop(x) {
    if (x >= 10) {
       console.log(x); // here if I add console.log(x) , x value is 10
        return (x); // next line if i return x output = undefined
    }
    forLoop(x + 1);
}

console.log(forLoop(0)); 

The output is "undefined" instead of 10.

Can anyone explain how recursion works in detail and how to fix the bug in my code?

Answer 1

If x is greater or equal to 10, the function returns x.

Otherwise, it calls itself but returns nothing .

You have to return something when the if fails.

function forLoop(x) {
    if (x >= 10) {
        return (x);
    }
    return forLoop(x + 1);
}