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

your validation should be occur before your event suppose you are going to submit your form.

anyway if you want this on onchange, so here is code.

function valid(id)
{
    var textVal=document.getElementById(id).value;
    if (!textVal.match(/\S/)) 
    {
        alert("Field is blank");
        return false;
    } 
    else 
    {
        return true;
    }
 }

Answer 2

function valid(id)
    {
        var textVal=document.getElementById(id).value;
        if (!textVal.match("Tryit") 
        {
            alert("Field says Tryit");
            return false;
        } 
        else 
        {
            return true;
        }
     }

Use this for expressing things

Answer 3

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>

(Or old live demo.)