Checking if a textbox is empty in Javascript

Question

This is my code which was supposed to raise an alert message if the textbox is left empty:

function a(id)
{
    var n=document.getElementById(id         


        

Answer 1

onchange will work only if the value of the textbox changed compared to the value it had before, so for the first time it won't work because the state didn't change.

So it is better to use onblur event or on submitting the form.

function checkTextField(field) {
  document.getElementById("error").innerText =
    (field.value === "") ? "Field is empty." : "Field is filled.";
}

(Or old live demo.)