javascript - 我无法解析 getElementsByClass 函数

Question

我正在尝试做一个成绩计算器网站，但我似乎无法将输入从字符串转换为整数。这是我的代码:

 <form  name="myform" action="" method="GET">
    <div>
        <label for="cmps200">CMPS 200</label>
        <input type="number" name="three" class="threeCredits">
        <br>
    </div>

    <div>
        <label for="cmps211">CMPS 211</label>
        <input type="number" name="three" class="threeCredits">
        <br>
    </div>

    <div>
        <label for="cmps212">CMPS 212</label>
        <input type="number" name="three" class="threeCredits">
        <br>
    </div>

    <div>
        <input id="btn" type="button" name="btn" value="Submit" onclick="myF()">
    <p> </p>

    </div>
</form>

<小时/>

function myF() {
    var courses3 = document.getElementsByClassName("threeCredits");
    var sum = 0;

    for(var i = 0; i < courses3.length; i++) {
        sum += parseInt(courses3[i]);
    }

    if(sum===0 || sum<=0){
        alert("Please enter valid inputs!");
    } else {
        alert(sum/9);
    }
}

每次我按下提交按钮时，我都会得到 NaN。请帮忙!

Answer 1

您的courses3[i]是一个元素，而不是它的值。使用courses3[i].value .

也在你的 if 中条件<=实际上还检查第一个，即 === 。所以你可以删除它

function myF() {
    var courses3 = document.getElementsByClassName("threeCredits");
    var sum = 0;

    for(var i = 0; i < courses3.length; i++) {
        sum += parseInt(courses3[i].value);
    }

    if( sum <= 0 ){
        alert("Please enter valid inputs!");
    } else {
        alert(sum/9);
    }
}

<form  name="myform" action="" method="GET">
    <div>
        <label for="cmps200">CMPS 200</label>
        <input type="number" name="three" class="threeCredits">
        <br>
    </div>

    <div>
        <label for="cmps211">CMPS 211</label>
        <input type="number" name="three" class="threeCredits">
        <br>
    </div>

    <div>
        <label for="cmps212">CMPS 212</label>
        <input type="number" name="three" class="threeCredits">
        <br>
    </div>

    <div>
        <input id="btn" type="button" name="btn" value="Submit" onclick="myF()">
    <p> </p>

    </div>
</form>