html - 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).value;
    if (n.length < 1)
    {
        window.alert("Field is blank");
        return false;
    }
}

The bug I'm getting is that the field is not getting verified onChange the first time. But when the text box is filled with some data and erased, now the OnChange fires, and the alert message is displayed. How can I fix this bug?

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.";
}

<input type="text" onblur="checkTextField(this);" />
<p id="error"></p>