使用 Javascript 自动求和输入值并显示

Question

Basically I want to update an Input field with the sum of all above Input Fields.

This is a part of HTML within tag:

<tr>
                <td width="20%">Admission Fee:</td>
                <td width="80%"><input onchange="findTotal()" type="text" class="input_box" name="admission_fee" id="fee" size="5" value="" maxlength="6" oninput="this.value = this.value.replace(/[^0-9]/, \'\');"></td>
            </tr>
            <tr>
                <td width="20%">Annual Fee:</td>
                <td width="80%"><input onchange="findTotal()" type="text" class="input_box" name="annual_fee" id="fee" size="5" value="" maxlength="6" oninput="this.value = this.value.replace(/[^0-9]/, \'\');"></td>
            </tr>
            <tr>
                <td width="20%">Paper Money Fee:</td>
                <td width="80%"><input onchange="findTotal()" type="text" class="input_box" name="paper_money_fee" id="fee" size="5" value="" maxlength="6" oninput="this.value = this.value.replace(/[^0-9]/, \'\');"></td>
            </tr>
            <tr>
                <td width="20%">Monthly Fee:</td>
                <td width="80%"><input onchange="findTotal()" type="text" class="input_box" name="monthly_fee" id="fee" size="5" value="" maxlength="6" oninput="this.value = this.value.replace(/[^0-9]/, \'\');"></td>
            </tr>
            <tr>
                <td width="20%">Remaining Balance:</td>
                <td width="80%"><input onchange="findTotal()" type="text" class="input_box" name="remaining_balance" id="fee" size="5" value="" maxlength="6" oninput="this.value = this.value.replace(/[^0-9]/, \'\');"></td>
            </tr>
            <tr>
                <td class="school_trow2" width="20%">Total Fee:</td>
                <td class="school_trow2" style="padding: 3px 0;" width="80%"><input type="text" class="input_box" style="background: #8CDFFF; border: 1px solid #006991; color: #000;" name="total_fee" id="total_fee" size="5" value="" disabled></td>
            </tr>

And this is the Javascript I am Using:

<script type="text/javascript">
        function findTotal()
        {
            var arr = document.getElementById(\'fee\');
            var tot=0;
            for(var i=0;i<arr.length;i++)
            {
                if(parseInt(arr[i].value))
                {
                    tot += parseInt(arr[i].value);
                }
            }
            document.getElementById(\'total_fee\').value = tot;
        }
        </script>

Any help would be appreciated.

Answer 1

This is what I've come up with.

• You are using same Id for multiple elements. I added the same class to the elements instead
• You are using <input type='text' then checking for numbers using regex. A better approach would be to just use <input type='number'
• Since maxlength does not work on type='number' , I have used max to handle 6 digit limit.

 function findTotal() { const fees = document.querySelectorAll(".fee"); const total = document.querySelector("#total_fee"); let sum = 0; fees.forEach(fee => { if(fee.valueAsNumber){ sum += fee.valueAsNumber; } }); total.value = sum; }

 <tr> <td width="20%">Admission Fee:</td> <td width="80%"><input onchange="findTotal()" type="number" class="input_box fee" name="admission_fee" value="" min='0' max='999999'></td> </tr> <tr> <td width="20%">Annual Fee:</td> <td width="80%"><input onchange="findTotal()" type="number" class="input_box fee" name="annual_fee" value="" min='0' max='999999'></td> </tr> <tr> <td width="20%">Paper Money Fee:</td> <td width="80%"><input onchange="findTotal()" type="number" class="input_box fee" name="paper_money_fee" value="" min='0' max='999999'></td> </tr> <tr> <td width="20%">Monthly Fee:</td> <td width="80%"><input onchange="findTotal()" type="number" class="input_box fee" name="monthly_fee" value="" min='0' max='999999'></td> </tr> <tr> <td width="20%">Remaining Balance:</td> <td width="80%"><input onchange="findTotal()" type="number" class="input_box fee" name="remaining_balance" value="" min='0' max='999999'></td> </tr> <tr> <td class="school_trow2" width="20%">Total Fee:</td> <td class="school_trow2" style="padding: 3px 0;" width="80%"><input type="text" class="input_box" style="background: #8CDFFF; border: 1px solid #006991; color: #000;" name="total_fee" id="total_fee" size="5" value="" disabled></td> </tr>

Answer 2

1. Never use the same id for more than one element. This defeats the whole purpose. :)

2. Change the class name on the total input field to something other than input_box . That way you can select all other <input> s by using document.querySelectorAll('.input_box') . Than traverse them as you did with arr and sum the values, etc.

        function findTotal()
        {
            var arr = document.querySelectorAll('.input_box');
            var tot=0;
            for(var i=0;i<arr.length;i++)
            {
                if(parseInt(arr[i].value))
                {
                    tot += parseInt(arr[i].value);
                }
            }
            document.getElementById(\'total_fee\').value = tot;
        }

Documentation on document.querySelectorAll()

Answer 3

Do what Philip and Ahsan Khan said about the HTML and using classes instead of ids for that.

Then use map to parse each value into a integer (or use parseFloat if you want float). Finally, use reduce to sum everything.

const findTotal = () => {
    const fees = [...document.querySelectorAll('.fee')].map(x => parseInt(x.value));
    const total = fees.reduce((a, b) => a + b);
    document.getElementById('total_fee').value = total;
}

Documentation on map

Documentation on reduce