报错：ReferenceError: Cannot access 'age' before initialization

                                      报错：ReferenceError: Cannot access 'X' before initialization

1、以下代码报错：ReferenceError: Cannot access 'age' before initialization

function fn (age){
    if (typeof age === 'undefined'){
        console.log(age);
        let age = 66;
    }
}

fn();

2、解决办法：

    将let换成var，let只能声明一次