Number from input box Javascript

Question

I\'m trying to get a number from an input box, but it returns an empty string as an alert. What do I miss?

Answer 1

You need to read the value of the input inside the function, not during page load. The following code will work.

var button = document.getElementsByClassName("btn")[0];

button.addEventListener("click", calculate);

function calculate() {
  var num = document.getElementById("input").value;
  alert(num);
}