HTML 和 Javascript 制作一个简单的加法计算器

Question

I'm trying to make a simple addition calculator. You put two values into the boxes and click the "+" sign and the third box has the sum. However, it looks like everything is right to me but when I click the + sign nothing happens

Answer 1

First you should change getElementsById() to getElementById() because there is only one id per element.

 <input type="text" id="box1"><br/> <input type="text" id="box2"><br/> <input type="text" id="+"><br/> <input type="button" value="+" onclick="calcSum()"><br/> <script> function calcSum(){ let box1 = document.getElementById("box1").value; let box2 = document.getElementById("box2").value; let sum = Number(box1) + Number(box2); document.getElementById("+").value = sum; } </script>