JavaScript 代码在我以一种方式编写时不运行，但在我稍作修改时运行

Question

有人可以指导我为什么我的代码在我以一种方式编写时不运行但在我稍加修改时运行吗？PS 我正在编写一个简单的 JavaScript 代码，它将根据变量在控制台中显示消息。这是不起作用的代码:

var age = "What is your age?";

prompt(age); 

if(age < 18) {
 console.log("you cant enter");
}

else if(age < 21) {
 console.log("you can enter but cannot drink");
}

else {
 console.log("Your can enter and drink!!");
}

但是当我以这种方式编写代码时(复制在下面)，它起作用了。有人可以解释一下我在这里做错了什么吗？

var age = prompt("What is your age?");

if(age < 18) {
 console.log("you can not enter");
}

else if(age < 21) {
 console.log("you can enter but cannot drink");
}

else {
 console.log("Your can enter and drink!!");
}

Answer 1

您不保存第一个代码段中 prompt 的结果。

var age = "What is your age?";

prompt(age); 

// at his point "age" has the value "What is your age?" and you check if age is smaller than < 18 and this is impossible
if(age < 18) {
 console.log("you cant enter");
}

....

总而言之，问题是您试图检查字符串是否小于 int