如何计算两个文本框并在另一个文本框中显示答案？

Question

I am trying to add the two text boxes and show the result in a third, whenever I try to add the third box, it makes it invalid. Any suggestions? Here is my code!

    <br>
    <br>
    <p4>Calculate Two Fields</p4>
    <p4 id="answer"></p4>
    <br>
    <br>

    Number 1<input type="text" id="num1" <br>
    <br>
    Number 2<input type="text" id="num2" <br>
    <br>
    <button onclick="calculate()">Calculate</button>

    <script>
        function calculate() {
            var field1 = document.getElementById(num1).value;
            var field2 = document.getElementById(num2).value;

            var result = parseFloat(field1) + parseFloat(field2)

            if (!isNaN(result))

            {
                document.getElementById("answer").innerHTML = "The answer is " + result;

            }
    </script>

Answer 1

Try.....

 $("#second").keyup(function() { var total = 0; $('.smtab_tot').each(function(_i, e) { var val = parseFloat(e.value); if (!isNaN(val)) total += val; }); $('#total').val(total); });

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> input 1 : <input type="number" class="smtab_tot" id="first"> <br> input 2 : <input type="number" class="smtab_tot" id="second"> <br> total : <input type="text" id="total">

Answer 2

I cant see any mistake except ; or } .

Its better to use onchange or other events events to remove clicking to get better ui/ux.

But you can do it with angularjs better.you can use ng-model for each input and in third input write {{model1+model2}} .

You can do it with vue.js too .the different is that you should use vmodel instead of ng-model .

Answer 3

getElementById('num1') here id should be in quote, otherwise it will be treated as variable.

Also you forgot the } at the end

 function calculate() { var field1 = document.getElementById('num1').value; var field2 = document.getElementById('num2').value; var result = parseFloat(field1) + parseFloat(field2); if (!isNaN(result)) { document.getElementById("answer").textContent= "The answer is " + result; } }

 <br> <br> <p4>Calculate Two Fields</p4> <p4 id="answer"></p4> <br> <br> Number 1<input type="text" id="num1" <br> <br> Number 2<input type="text" id="num2" <br> <br> <button onclick="calculate()">Calculate</button>