can't get the output from javascript

Question

var weightkg=document.getElementById('weight').value;

    var heightinm=document.getElementById('height').value;
    
    function bmival (weightkg,heightinm){

        var hout=heightinm*2
        var output=weightkg/hout
        //make a full number
             // var r= Math.trunc(o)
             
         if (output<=18.5){
            return document.getElementById('print').innerHTML=`Your BMI is ${output} you are underweight` ;
         }
 
         else if(output>18.5 && o<25.5){
            return document.getElementById('print').innerHTML=`Your BMI is ${output} You come under fit catogery`;
         }
 
         else{
            return document.getElementById('print').innerHTML=`Your BMI is ${output} you are overweight and obese`;
         }
     }

[i am making a bmi cal that take input from user but i am getting a error and don't know what i am doing wrong]

** this is js code and when i run i get a NaN instead of Number **

How are you calling this code? You need to get the values of the inputs when they click the button to calculate, not when the page starts. — Barmar
– Barmar, Commented Aug 29, 2022 at 16:45
The global variable names weightkg and heightinm are the same as your function argument names, which is really confusing. — kmoser
– kmoser, Commented Aug 29, 2022 at 16:47
Does this answer your question? HTML input type="number" still returning a string when accessed from javascript — Jared Smith
– Jared Smith, Commented Aug 29, 2022 at 16:50

Charles Kasasira · Accepted Answer · 2022-08-29 16:49:09Z

1

The values from an input field are strings so you must convert them into numbers


var heightinm = +document.getElementById('height').value; // one way to do it.

answered Aug 29, 2022 at 16:49

Charles Kasasira

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Comments

Ahmet Ulutaş · Accepted Answer · 2022-08-29 17:05:31Z

The value you get from

var weightkg=document.getElementById('weight').value;

seems to be a string instead of number. You need to convert values to do Math operations on them. NaN tells you output is not a number. Turn your values to number with parseInt method.

var weightkg = parseInt(document.getElementById('weight').value);

or you can just put a "+" to convert a string into number

var weightkg = +document.getElementById('weight').value;

For Example.

const input = document.getElementById('input');
const defaultStringInput = document.getElementById('input').value;
const inputConverted = parseInt(document.getElementById('input').value);
const inputConverted2 = +document.getElementById('input').value;
input.addEventListener('change', () => {

  console.log(typeof defaultStringInput); // string
  console.log(typeof inputConverted); // number
  console.log(typeof inputConverted2); // number
});

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