text in textbox

how would you make a function that cheks if any text is in a text box.

if ( document.formName.fieldName.value = "" )
{
alert("field is empty");
} else {
alert("field is not empty");
}

If you want to make sure the field has something *other* than just spaces, just strip out the spaces:

if ( document.formName.fieldName.value.replace(/\s/g,"") = "" )

Thanks, i wonder why i didint think of that...