How to verify a form is empty ? PHP or JS

Please, I'm a newbie in PHP, and created my web site, with a text form, i can verify with JQuery if the txt form is empty or not with the following code :

    $(document).ready(function()
    {
        $('#formLike').ajaxForm({                       
                target:         '#content',
                beforeSubmit:   validateForm
        }); 

        //hide error containers
        $("#txtform_error").hide();

    });

    function validateForm开发者_开发百科()
    {
        $("#txtform_error").empty().hide();

        var txtform         = $("#txtform").val();
        var errors              = 0;

        if (txtform == null || txtform == ''  || txtform == ' ')
        {
            $("#txtform_error").show().append("Please Write a Message Before Clicking : Like It");
            document.formLike.txtform.focus();
        }
        else
        {
        document.formLike.submit();
        }


    }

How to verify that the txt form is not empty, and there is not only white-spaces in the field, because here after submitting many white-spaces, the text is posted to the action page.

Sorry for my bad english.

Thanks in advance.

Replace this line

if (txtform == null || txtform == ''  || txtform == ' ')

With this line

if ($.trim(txtform) == "")

$.trim removes unnecessary spaces so it will get trimmed to "" if someone enters only white space.

[EDITED]

for the checking:

if (txtform == null || txtform == ''  || txtform == ' ')

must be

if (!txtform || txtform.replace(/\s/g, '') == '') 

or

if (!txtform || !txtform.replace(/\s/g, '')) 

or

if (!txtform || !jQuery.trim(txtform)) //trimmed only

This means, that the input must contain atleast 1 non-space character