防止isNaN隐式转换为数字

Question

我正在学习一些JavaScript并遇到了一个怪癖,并想知道是否有人知道如何覆盖这种行为.我希望能够测试传递给函数的值是否为实数,并且我认为===用于isNaN()检查会处理这个问题,但事实并非如此.

功能示例:

var foodDemand = function(food) {
    if (isNaN(food) === false) {
        console.log("I can't eat " + food + " because it's a number");
    } else {
        console.log("I want to eat " + food);
    }
};

我测试了这个:

// behaves as expected
foodDemand("steak");
foodDemand(999999999);
foodDemand(0.0000001337);
foodDemand([1]);
foodDemand(undefined);
foodDemand(NaN);
foodDemand({});
// converts non-number to a number
foodDemand("42");
foodDemand("");
foodDemand(null);
foodDemand([]);
foodDemand("\n");

输出(斜体表示意外结果):

I want to eat steak
I can't eat 999999999 because it's a number
I can't eat 1.337e-7 because it's a number
I can't eat 1 because it's a number
I want to eat undefined
I want to eat NaN
I want to eat [object Object]
I can't eat 42 because it's a number
I can't eat  because it's a number
I can't eat null because it's a number
I can't eat  because it's a number
I can't eat 
 because it's a number

有没有办法让isNaN()更严格？

Answer 1

isNaN的目的不是测试某些东西是不是数字,而是测试某些东西是否为数字NaN(因为NaN===NaN在JavaScript中返回false,你不能使用相等).

你应该使用typeof,然后是isNaN:

if((typeof food)==="number" && !isNaN(food))

你可能会问,为什么NaN不等于NaN？这是JavaScript的臭名昭着的怪癖吗？

事实证明这种行为是有充分理由的.无法返回实际结果的数学运算,即使是无限,也不会抱怨并抛出错误.他们只是回归NaN.例如,0/0,sqrt(-1),acos(2).拥有不是很奇怪Math.sqrt(-1) === 0/0吗？所以NaN甚至不等于自己.因此,isNaN如果您确实想要检查值是否为NaN,则需要原语.