计算输入的值并将结果设置在另一个字段中

Question

I have a value 1000 and two input fields like X and Y .
If I put a value 300 on X then the value calculate with 1000 and automatically fill the Y field with 700 . Same as if I put the Y field first then X value will calculate automatically. The value can be anything below 1000 . If it's over 1000 then I want to show a alert message.

Answer 1

In the following code we create 2 inputs and we listen for a change event on both. When one input value changes, we set the other's value to 1000 - value.

<p>
First
<input min="0" max="1000" type="number" id="first">
</p>
<p>
  Second
<input  min="0" max="1000"  type="number"  id="second">
</p>

Js (with jquery):

$("#first").change((el)=>{
   $("#second").val(1000 - el.target.value);
});
$("#second").change((el)=>{
   $("#first").val(1000 - el.target.value);
});

https://codepen.io/Pocciox/pen/ExxzVXz