how to apply js on specific place?

Question

how to get the input from the textbox and the apply some javascript on it
like
if get a number from user return the result odd or even???
how to do this ??

Answer 1

first you use document.getElementById("yourTextboxID").value
to get the value of the textbox,
after that you you use modulo to check if the number is even or not
function isOdd(num) { return num % 2;}