Javascript闭包(函数)

Question

​

function outside() {
    let out = 0;
    function inside() {
        out += 1;
    }
    return inside;
}

let ref = outside();
console.log(ref());

​

为什么当打印出而不是内部函数的值(即1)时，会出现未定义的情况？

Answer 1

inside函数必须返回值。

​

function outside() {
    let out = 0;
    function inside() {
        return ++out;
    }
    return inside;
}

let ref = outside();
console.log(ref());

​