Change Placeholder Text using jQuery

I am using a jQuery placeholder plugin( I need to change the placeholder text with the change in dropdown menu. But it is not changing. Here is the code:

$(function () {
    $('input[placeholder], textarea[placeholder]').placeholder();
    $('#serMemdd').change(function () {
        var k = $(this).val();
        if (k == 1) {
            $("#serMemtb").attr("placeholder", "Type a name (Lastname, Firstname)").placeholder();
        else if (k == 2) {
            $("#serMemtb").attr("placeholder", "Type an ID").placeholder();
        else if (k == 3) {
            $("#serMemtb").attr("placeholder", "Type a Location").placeholder();

My Html:

<div class="filterbox">
        <select name="ddselect" id="serMemdd">
            <option value="1" selected="selected">Search by Name</option>
            <option value="2">Search by ID</option>
            <option value="3">Search by Location</option>
        <input id="serMemtb" type="text" style="width: 490px" placeholder="Type a name    (Lastname, Firstname)" />
        <input id="seMemBut" type="button" value="Search" />

Can anyone figure this out?


  $('form').find("input[type=textarea], input[type=password], textarea").each(function(ev)
      if(!$(this).val()) { 
     $(this).attr("placeholder", "Type your answer here");

Copy and paste this code in your js file, this will change all placeholder text from whole site.