如何在此脚本代码中使此计算和变量正确？

Question

I feel like I'm progressing a little, I still have difficulties figuring out what to do when I'm stuck with Javascript. It's very hard but I need to get this coding done urgently.. so any help is greatly appreciated.

It's really simple, I want to make my own converter from Kelvin, Celsius and Fahrenheit. So I made these 3 variables, but I kind of realised they need their own formula, so do I need a different variable for the result? And if so where does it go? All these functions are so confusing. This is my code.

        <form>
 Kelvin is
  <input id="kelvin" size="7" maxlength="5" type="text" placeholder="vul in" />
  <p></p>
  Celsius is
  <input id="celsius" size="7" maxlength="9" type="text" placeholder="vul in" />
  <p></p>
Fahrenheit is
<input id="fahrenheit" size="7" maxlength="9" type="text" placeholder="vul in" />
  <p></p>
  <input id="calculate" type="button" value="Bereken!" />

</form>



<div id="calc">Dit is kelvin
  <p></p>dit is celsius

dit is fahrenheit

and then the script

<table cellSpacing=0 cellPadding=0 width=250 border=0>

document.getElementById('calculate').addEventListener('click', function() {



var kel= document.getElementById("kelvin").value;
var cel = document.getElementById("celsius").value;
var far = document.getElementById("fahrenheit").value;
var div = document.getElementById('calc');

if (( kel < 0 ||  cel < -273 || far < -459 ||  isNaN(kel) || isNaN(bev)) {
    div.innerHTML = "Not valid!";
    return;
  }

  kel = parseInt(kelvin); cel = parseInt(celsius); far = parseInt (fahrenheit);

  var far =  (cel * (9/5) + 35;
  var kel = cel + 273;
  var cel = kel - 273;
  var cel = (far -32)*(5/9);



  if (far = kel ) {
    var text = "hello? what to do here";

  }

 div.innerHTML = "Het is  <b>" + kelvin+ "</b> Kelvin <p></p> en het is <b>" + celcius + "</b>" en het is  <b>" + fahrenheit + "</b>";
 }, false); 

Answer 1

First of all

if (far = kel ) {
    var text = "hello? what to do here";
}

should be

if (far === kel ) {
    var text = "hello? what to do here";
}

= is used to define variables eg. var a = 10;

=== is used to compare two values

Also, you put

<table cellSpacing=0 cellPadding=0 width=250 border=0>

in the middle of the script. Which I hope was a mistake.

Which is best written

<table cellspacing='0' cellpadding='0' width='250' border='0'>

To be compliant with newer stricter XHTML standards.

Also, this:

if (( kel < 0 ||  cel < -273 || far < -459 ||  isNaN(kel) || isNaN(bev)) {
    div.innerHTML = "Not valid!";
    return;
}

needs to be replaced by this:

if ( kel < 0 ||  cel < -273 || far < -459 ||  isNaN(kel) || isNaN(cel) || isNaN(far)) {
    document.getElementById('calc').innerHTML = "Not valid!";
}

And this:

 kel = parseInt(kelvin); cel = parseInt(celsius); far = parseInt (fahrenheit);

Should read:

kel = parseInt(document.getElementById("kelvin").value); cel = parseInt(document.getElementById("celcius").value); far = parseInt (document.getElementById("fahrenheit").value);

Answer 2

Claies has a good point too.

if(kel != ''){
    //Kelvin is the chosen one
}else if(far != ''){
    //Fahrenheit is the chosen one
}else if(cel != ''){
    //Celcius is the chosen one
}else{
    //User hasn't written anything
    alert('You need to write something to convert!');
}