javascript - 简短的 Javascript 程序问题(错误输出)

Question

const HIGH_AGE = 70, MAX_AGE = 120, BABIE_AGE=4, TEEN_AGE=16;

function main ()

{

 var age;  
    age = Number(prompt('Enter your age:')); //set prompt box ask user's age

    if (age < BABIE_AGE || age > MAX_AGE)//if user user's age are below "0" or above "120" 
        alert('Please Enter Age Within the Range between 0-120!');//output: must enter age in valid age range

    else if (isNaN(age) == true || !age)
        alert('please enter a valid entry');   

    else if ((age >= HIGH_AGE) || (age >= 0 && age <= BABIE_AGE))//if age between 0-4 or above 70 
        alert('You may travel for free');//output: they can travel for free     

    else if (age >= CHILDREN_AGE && age <= TEEN_AGE )//if user's age are under 16 
        alert('You may travel with a half price ticket');//output they can travel for half-price

    else 
        alert('You must travel with a full price ticket'); //others all travel with full price
}

Answer 1

使用isNaN功能:

if (isNaN(age)) {
    // ... age is not valid number
}

Number(prompt('...')) 如果无法将输入解释为数字，将返回 NaN 值。