javascript - 年龄计算器 : checking for a blank input or a string input

Question

我有一个功能，可以通过询问您的问题来确定您的年龄。我想取消该功能，并在用户输入字符串值或根本不输入任何内容时发出警报。

这是我到目前为止的代码:

<button id="btn"> Calculate Age </button>

<p id="para"></p>


document.getElementById("btn").addEventListener("click", ageCalc);


function ageCalc () {

    // Calculate year of birth

    var year = prompt("What year were you born?");
    if (parseInt(year) < 1917) {
        return alert("Please enter a valid year");
    }

    // Calculate month of birth

    var month = prompt("Numerically, what month were you born?");

    if (parseInt(month) > 12 || parseInt(month) < 1 ) {
        return alert("Please enter a valid month!");
    }


    // Calculate day of birth

    var day = prompt("What day were you born?");

    if(parseInt(day) > 32 || parseInt(day) < 1) {
        return alert("Please enter a valid day!");
    }

    // Calculate age based on user input

    var presentDate = new Date ();
    var birthDate = new Date(year,month,day);
    var age = (presentDate - birthDate) / 1000 / 60 / 60 / 24 / 365;

    return document.getElementById("para").innerHTML = "You are " + Math.floor(age) + " years old.";
}

这里正确的做法是什么？我认为它将以某种方式调整 if 语句来检查字符串或空白语句，但我有点迷失了。大家有什么想法吗？

Answer 1

您可以通过简单添加 if 检查来排除 null/未定义/空 year 值。另外，始终为 parseInt 添加第二个radix 参数。方法:

var year = prompt("What year were you born?");
if (!year || parseInt(year, 10) < 1917) {       
   return alert("Please enter a valid year");
}

您可以对月和日执行相同的操作。