JavaScript returns NaN even if input is an integer

Question

I am typing an integer in the input box and it still returns 'NaN'.

function goldenFunctiona() {
  a = document.getElementById("sidea");
  parseInt(a, 10);
  b = ((a + a) * (Math.pow(5, 0.5))) / 2;
  document.getElementById("b").innerHTML = b;
}

<div id="top">
  <p>Side a =</p>
  <input id="sidea" type="number">
  <button id="button" onclick="goldenFunctiona()" type="button">Find side b</button>
  <p id="b"></p>
</div>

I don't know what's going wrong but it's probably something really simple. Thanks in advance.

To clarify the below answers, ALL form elements are ASCII strings. If you need to get an integer value, you need to do a conversion. — durbnpoisn
– durbnpoisn, Commented Oct 26, 2015 at 18:25
a is the element, not the input value. Try parseInt(a.value, 10) — wintvelt
– wintvelt, Commented Oct 26, 2015 at 18:26

DontVoteMeDown · Accepted Answer · 2015-10-26 18:40:33Z

4

document.getElementById("sidea") doesn't returns a number, but an element. Use document.getElementById("sidea").value instead to get the element value.

So:

function goldenFunctiona() {
    var sideaVal = document.getElementById("sidea").value;

    var a = parseInt(sideaVal , 10); // Get parseInt's return value or 'a' will still be a string
    var b = ((a + a) * (Math.pow(5, 0.5))) / 2;

    document.getElementById("b").innerHTML = b;
}

edited Oct 26, 2015 at 18:40

answered Oct 26, 2015 at 18:24

DontVoteMeDown

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3 Comments

wintvelt Over a year ago

Cleaner even would be a = parseInt(document.getElementById("sidea").value), 10); (Reassigning variable a to completely different variable type is not so clean).

DontVoteMeDown Over a year ago

@wintvelt now its clean.

hanshenrik Over a year ago

since its not HTML, you could use textContent, its faster and safer.. *although i don't see how this function could return anything dangerous in the first place

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