Error when multiplying input value in a variable

November 25, 2021

I have 2 lists (conversion from kilometers to miles etc.). When I’m trying to use input value to calculate (so "X * 1.609" for kilometers to miles) I have an error NaN.

const inputPlace = parseInt(document.getElementById("inputPlace").value);

const config = {
 "kilometers": {
    "miles": inputPlace * 1.609,
    "yards": "Convert km to yd",
    "feet": "Convert km to ft",
    "inches": "Convert km to in"
  },
  "meters": {
    "miles": "Convert m to mi",
    "yards": "Convert m to yd",
    "feet": "Convert m to ft",
    "inches": "Convert m to in"
  },
  "centimeters": {
    "miles": "Convert cm to mi",
    "yards": "Convert cm to yd",
    "feet": "Convert cm to ft",
    "inches": "Convert cm to in"
  },
  "milimeters": {
    "miles": "Convert mm to mi",
    "yards": "Convert mm to yd",
    "feet": "Convert mm to ft",
    "inches": "Convert mm to in"
  }
}

document.getElementById("btn").addEventListener("click", function(){
   const metricValue = document.getElementById("metric").value;
   const impValue = document.getElementById("imperial").value;
   
   document.getElementById("aaa1").innerHTML = config[metricValue][impValue].toFixed(2);
});

              <input type="number" id="inputPlace">
                
                <select name="metric" id="metric">
                  <option value="kilometers">km</option>
                  <option value="meters">m</option>
                  <option value="centimeters">cm</option>
                  <option value="milimeters">mm</option>
                </select>

                <select name="imperial" id="imperial">
                  <option value="miles">mi</option>
                  <option value="yards">yd</option>
                  <option value="feet">ft</option>
                  <option value="inches">in</option>
                </select>

                <button id="btn">Click</button>
                <p id="aaa1">Placeholder</p>

(Please only look at first example – km to mi)
How to fix it?

>Solution :

Well, this one is simple. In the first line of your code, you are getting the value of the input, which is a blank string (the user hasn’t entered anything yet! You’re executing that line once the page loads), which when you try to convert to an int results in "Not a Number". Instead, you should get the value of the number when you press the click button, not once the page loads (you also have to create a function to dynamically calculate the value):

function calc(value) {
  // creating a function to re-calculate the value
  const config = {
    "kilometers": {
      "miles": value * 1.609,
      "yards": "Convert km to yd",
      "feet": "Convert km to ft",
      "inches": "Convert km to in"
    },
    "meters": {
      "miles": "Convert m to mi",
      "yards": "Convert m to yd",
      "feet": "Convert m to ft",
      "inches": "Convert m to in"
    },
    "centimeters": {
      "miles": "Convert cm to mi",
      "yards": "Convert cm to yd",
      "feet": "Convert cm to ft",
      "inches": "Convert cm to in"
    },
    "milimeters": {
      "miles": "Convert mm to mi",
      "yards": "Convert mm to yd",
      "feet": "Convert mm to ft",
      "inches": "Convert mm to in"
    }
  }
  return config;
}

document.getElementById("btn").addEventListener("click", function() {
  const metricValue = document.getElementById("metric").value;
  const impValue = document.getElementById("imperial").value;
  const inputPlace = parseInt(document.getElementById("inputPlace").value.replaceAll(",", "").replaceAll(" ", ""));

  document.getElementById("aaa1").innerHTML = calc(inputPlace)[metricValue][impValue].toFixed(2); // calling a function that returns an object instead of just using the object
});

<input type="number" id="inputPlace">

<select name="metric" id="metric">
  <option value="kilometers">km</option>
  <option value="meters">m</option>
  <option value="centimeters">cm</option>
  <option value="milimeters">mm</option>
</select>

<select name="imperial" id="imperial">
  <option value="miles">mi</option>
  <option value="yards">yd</option>
  <option value="feet">ft</option>
  <option value="inches">in</option>
</select>

<button id="btn">Click</button>
<p id="aaa1">Placeholder</p>