jquery is not working

I am using jquery with ajax. Sometimes, It is giving error $ is not defined.

This is my code:

<script language="javascript" type="text/javascript">
  var base_path="<? echo $this->baseUrl().'/'; ?>";

    function checkemail()
    {
                var email=document.getElementById('comp_email').value;
                //alert(email);
        if(email!='')
        {

          $.ajax({
                                 url:  base_path + "admin/jobs/emailcheck/",
                                data: "email="+email,
                                type: 'GET',
                         success: function (resp) 
                         {

                                         //alert(resp);

                                        $("#valid_email").html(resp);

                                        //alert($("#valid_email table tr td").text());
                                        if($("#valid_email table tr td").text()=='This firm is not exist in database. Firstly register this firm.')
                                        {
                                                //alert('ok');
                                                $.ajax({
                                                         url:  base_path + "admin/profile/firmadd/",
                                                        data:"flag=jobsController",
                                                        type: 'POST',
                                                 success: function (resp) 
                                                 {
                                                        document.getElementById('firm_add_form').style.display='';
                                                        //alert(resp);
                                                                $("#firm_add_form").html(resp);
                                                                document.getElementById('register_typ').focus();
                                                                return false;
                                                 },
                                                        error: function(e){  alert('Error: '+e);  }  
                                                });                                     
                                        }
                                        else
                                        {
                                                document.getElementById('firm_add_form').style.display='none';
                                                document.getElementById('valid_email').style.display='none';
                                                var comp_name = resp.substring(0,resp.indexOf(',',0));
                                                var comp_web = resp.substring(resp.indexOf(',',0)+1);
                                                document.getElementById('comp_name').value = comp_name;
                                                document.getElementById('comp_web').value = comp_web;
                                                return true;
                                        }
                         },
                                error: function(xhr ,e){ 
                                        alert(xhr.readyState); 
                                        alert('Error: '+e);  }  
                        });
                }
  }
 </script>

This function is called on onblur in a textbox and called on onclick on submit button in same form.

But when I call it on onblur it is working properly but when I call it on onclick then it is giving error $ is not defined.

And when I gives alert(email) then it is working properly on onclick on submit button.

my form is below:

        <form id="addfrm" enctype="application/x-www-form-urlencoded" method="post" action=""
  name="">
    <table align="center" class="tbcss" width="100%" cellspacing="0" cellpadding="0">
      <tr>
        开发者_StackOverflow社区<td align="right" valign="top" width="15%"><label for="comp_email" class=
        "optional">Company Email:</label></td>

        <td class="element" width="26%" valign="top"><input type="text" name="comp_email"
        id="comp_email" value="" size="35" onblur="return checkemail()"><span id=
        "valid_email" align="left" width="55%"></span></td>

        <td align="right" valign="top" width="15%"><label for="comp_name" class=
        "required">Company Name:</label></td>

        <td class="element" width="26%" valign="top"><input type="text" name="comp_name"
        id="comp_name" value="" size="35"></td>
      </tr>

      <tr>
        <td id="firm_add_form" colspan="4"></td>
      </tr>

      <tr>
        <td align="right" valign="top" width="15%"><label for="comp_web" class=
        "optional">Company Website:</label></td>

        <td class="element" width="26%" valign="top"><input type="text" name="comp_web"
        id="comp_web" value="" size="35"></td>

        <td align="right" valign="top" width="15%"><label for="category" class=
        "required">Job Category:</label></td>

        <td class="element" width="26%"><select name="category" id="category">
          <option value="" label="Select Category">
            Select Category
          </option>

          <option value="Architecture" label="Architecture">
            Architecture
          </option>

          <option value="Manufacturing" label="Manufacturing">
            Manufacturing
          </option>

          <option value="IT" label="IT">
            IT
          </option>
        </select></td>
      </tr>

      <tr>
        <td align="right" valign="top" width="15%"><label for="job_title" class=
        "optional">Job Title:</label></td>

        <td class="element" width="26%" valign="top"><input type="text" name="job_title"
        id="job_title" value="" size="35"></td>

        <td align="right" valign="top" width="15%"><label for="contact_prsn" class=
        "optional">Contact Person:</label></td>

        <td class="element" width="26%" valign="top"><input type="text" name=
        "contact_prsn" id="contact_prsn" value="" size="35"></td>
      </tr>

      <tr>
        <td align="right" width="15%"><label for="close_date" class="optional">Closing
        Date:</label></td>

        <td class="element" width="26%"><select name="close_date" id="close_date">
          <option value="" label="Date">
            Date
          </option>

          <option value="1" label="01">
            01
          </option>

          <option value="2" label="02">
            02
          </option>

          <option value="3" label="03">
            03
          </option>

          <option value="4" label="04">
            04
          </option>

          <option value="5" label="05">
            05
          </option>

          <option value="6" label="06">
            06
          </option>

          <option value="7" label="07">
            07
          </option>

          <option value="8" label="08">
            08
          </option>

          <option value="9" label="09">
            09
          </option>

          <option value="10" label="10">
            10
          </option>

          <option value="11" label="11">
            11
          </option>

          <option value="12" label="12">
            12
          </option>

          <option value="13" label="13">
            13
          </option>

          <option value="14" label="14">
            14
          </option>

          <option value="15" label="15">
            15
          </option>

          <option value="16" label="16">
            16
          </option>

          <option value="17" label="17">
            17
          </option>

          <option value="18" label="18">
            18
          </option>

          <option value="19" label="19">
            19
          </option>

          <option value="20" label="20">
            20
          </option>

          <option value="21" label="21">
            21
          </option>

          <option value="22" label="22">
            22
          </option>

          <option value="23" label="23">
            23
          </option>

          <option value="24" label="24">
            24
          </option>

          <option value="25" label="25">
            25
          </option>

          <option value="26" label="26">
            26
          </option>

          <option value="27" label="27">
            27
          </option>

          <option value="28" label="28">
            28
          </option>

          <option value="29" label="29">
            29
          </option>

          <option value="30" label="30">
            30
          </option>

          <option value="31" label="31">
            31
          </option>
        </select> <span class="element"><select name="close_month" id="close_month">
          <option value="" label="Month">
            Month
          </option>

          <option value="01" label="Jan">
            Jan
          </option>

          <option value="02" label="Feb">
            Feb
          </option>

          <option value="03" label="Mar">
            Mar
          </option>

          <option value="04" label="Apr">
            Apr
          </option>

          <option value="05" label="May">
            May
          </option>

          <option value="06" label="Jun">
            Jun
          </option>

          <option value="07" label="Jul">
            Jul
          </option>

          <option value="08" label="Aug">
            Aug
          </option>

          <option value="09" label="Spt">
            Spt
          </option>

          <option value="10" label="Oct">
            Oct
          </option>

          <option value="11" label="Nov">
            Nov
          </option>

          <option value="12" label="Dec">
            Dec
          </option>
        </select></span> <span class="element"><select name="close_year" id="close_year">
          <option value="" label="Year">
            Year
          </option>

          <option value="2009" label="2009">
            2009
          </option>

          <option value="2010" label="2010">
            2010
          </option>

          <option value="2011" label="2011">
            2011
          </option>

          <option value="2012" label="2012">
            2012
          </option>

          <option value="2013" label="2013">
            2013
          </option>

          <option value="2014" label="2014">
            2014
          </option>

          <option value="2015" label="2015">
            2015
          </option>

          <option value="2016" label="2016">
            2016
          </option>

          <option value="2017" label="2017">
            2017
          </option>

          <option value="2018" label="2018">
            2018
          </option>

          <option value="2019" label="2019">
            2019
          </option>

          <option value="2020" label="2020">
            2020
          </option>

          <option value="2021" label="2021">
            2021
          </option>
        </select></span></td>

        <td align="right" valign="top" width="15%"><label for="location" class=
        "required">Location:</label></td>

        <td class="element" width="26%"><input type="text" name="location" id="location"
        value="" size="35"></td>
      </tr>

      <tr>
        <td align="right" valign="top" width="15%"><label for="job_detail" class=
        "optional">Job Details:</label></td>

        <td class="element" width="26%" valign="top">
        <textarea name="job_detail" id="job_detail" cols="30" rows="5">
</textarea></td>

        <td align="right" valign="top" width="15%"><label for="notes" class=
        "required">Notes:</label></td>

        <td class="element" width="26%">
        <textarea name="notes" id="notes" cols="30" rows="5">
</textarea></td>
      </tr>

      <tr>
        <td align="right" valign="top" width="15%"><label for="block" class=
        "optional">Block:</label></td>

        <td class="element" width="26%"><input type="hidden" name="block" value=
        "N"><input type="checkbox" name="block" id="block" value="Y"></td>

        <td align="right" valign="top" width="15%"><label for="source" class=
        "optional">Job Source/Link:</label></td>

        <td class="element" width="26%" valign="top"><input type="text" name="source" id=
        "source" value=""></td>
      </tr>

      <tr>
        <td align="center" colspan="4"><input type="submit" name="add" id="add" value=
        "Add" onclick="return checkemail();"> <button name="back" id="back" type="button"
        onclick="window.location='/allindiazend/admin/jobs/list'">Back</button></td>
      </tr>
    </table>
  </form>

can any body help me plz.

$ is defined by the jQuery library. You are therefore, presumably, not successfully including the library on your page.

• Check you have a <script> element that includes it and is not 404 erroring.
• Check that you do so earlier in the page then any attempts to use it
• Check you are not defering the request for the script
• Check that the browser is making the request (in the Net tab of whatever debug tool (e.g. Firebug) you use

Your jQuery is not getting loaded properly sometimes. Ideally, use Google's CDN to load it.

You should put all of jQuery's scripts in a document ready block as such:

<script type="text/javascript">
    $(document).ready(function(){
            //call jQuery enabled functions here
        });
</script>

This makes sure jQuery is loaded (and $ is defined) before executing