Encounter a parameter validation error

Just a quick question. I have a JS function that takes a parameter as input. If the passed value happens to be NULL, I want to handle it accordingly. However, my limited experience with JS is making it difficult for me to use the correct syntax. Here's what I have so far. Can you help me change the syntax? The function has more code besides this snippet, and it works fine when I don't check for NULL. The issue lies in the last line due to using a reserved word, but I'm unsure how to resolve it.

<script type="text/javascript">

    //Pass UserName from text box on form to Ajax call 
  function CheckUserName(UserName_element) {

      var UserName = try { UserName_element.value; } catch (e) { };

For those wondering: This is a JavaScript function inside a VBScript Sub (unfortunately, the entire site is built in classic ASP).

    Sub UserNameValidation_Entry()
%>
<div id="username_validation" style="width:15px;position:relative;float:right;">
<img id="valid_UserName_image" src="<%=UrlForAsset("/images/tick.png")%>" border="0" style="display:none;" alt="User Name is Available." 
    title="User Name is Avaliable." />
<img id="invalid_UserName_image" src="<%=UrlForAsset("/images/icon_delete_x_sm.png")%>" border="0" style="display:none;" alt="User Name Already Exists." 
    title="User Name Already Exists." />
</div>

<script type="text/javascript">

        //Pass UserName from text box on form to Ajax call 
      function CheckUserName(UserName_element) {

          var UserName = UserName_element.value; 
          var UserName = try { UserName_element.value; } catch (e) { };


        $j.ajax({
            data: { action: 'CheckUserName', p_UserName: UserName },
            type: 'GET',
            url: 'page_logic/_check_username_ajax.asp',
            success: function (result) {

                //If user exists return X out, if not return green checkmark
                if (result == "True") {
                    try { valid_UserName_image.style.display = "none"; } catch (e) { };
                    try { invalid_UserName_image.style.display = "inline"; } catch (e) { };
                }
                else {
                    try { valid_UserName_image.style.display = "inline"; } catch (e) { };
                    try { invalid_UserName_image.style.display = "none"; } catch (e) { };
                    }
                }
            }
        );
        //return false;
    }
</script>

Here's where the function is called.

           <tr class="required_field">
            <td class="empty"></td>
            <td><b>Username:</b></td>
            <td class="label_value_separator"></td>
            <td>
                <input type='text' name="username" size="24" maxlength="50" value="<%=Session("s_username") %>" onblur="CheckUserName(this);">
                <% Call UserNameValidation_Entry() %>

        </tr>

Answer №1

As mentioned by minitech, there may be no need to utilize a try/catch block in this situation. This is typically only necessary when trying to access an object property that could potentially be "undefined", or when attempting to parse JSON that may not be valid.

A simple solution would be to

if ( username !== null ) {
  // Send AJAX request
} else {
  // Send error message to UI
}

There are various other methods for detecting JavaScript null-like values discussed in this response.

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