Need Very Basic Javascript Form Validation for Name and Email Field

I am trying to validate few fields in my form, I dont want to change anything becasue everything is link to each other and I dont want to mess anything. Basically all I want is to validate name and email field and Once successful then I will move to other fields. I try to do it with below javascript code but it didnt work for me.

NOTE: I need to do it with Javascript not Jquery, and I need a basic Javascript not complicated because I am completely Novice to Javascript. ANy help will be appreciated.

This Is Fiddle Link

 var frmvalidator = new Validator("form1");
 frmvalidator.addValidation("FirstName","req","Please enter your First Name");
 frmvalidator.addValidation("FirstName","maxlen=20",
        "Max length for FirstName is 20");
 
 frmvalidator.addValidation("LastName","req");
 frmvalidator.addValidation("LastName","maxlen=20");
 
 frmvalidator.addValidation("Email","maxlen=50");
 frmvalidator.addValidation("Email","req");
 frmvalidator.addValidation("Email","email");

<h1> Contact Form</h1>
                        <form id="form1" class="campus"  method="post">
                                <div class="form_description">
                                        <h2>User Feedbacks</h2>
                                        <p>Please give us your feedbacks.</p>
                                </div>    
                                
                                <ul>
                                        <li>
                                                <label class="description" >Name*</label>
                                 
                                                <input type="text" name="FullName" id="FirstName" maxlength="50" size="8" />
                                                <label for="FirstName"> First </label>
                                         
                                                <input type="text" name= "user" id="LastName"  maxlength="50" size="8"/>
                                                <label for="LastName"> Last </label>
                                        </li>             
                        
                                        <li >
                                                <label for="Email" class="description">Email*:</label>
                                                <input type="email" name="Email"  id="Email" maxlength="55"/>
                                        </li>     
                                
                                        <li>
                                                <label class="description" >Reason for Contacting:</label>
                                
                                                <input name="choice" id="Hospitality" type="checkbox" value="1"/>
                                                <label  for="Hospitality">  About Website </label>
                                                <input name="choice" id="Technology" type="checkbox" value="1" />
                                                <label for="Technology"> About Deals </label>
                                                <p class="guidelines" ><small>Reason for contacting. Please select all that are applicable</small></p> 
                                        </li>     
                             <li>
                                                        <label class="description" >Will you Recommend us to anyone.</label>
                                                <select> 
                                                                <option value="" ></option>
                                                                <option value="1" >Yes</option>
                                                                <option value="2" >No</option>
                                                                <option value="3" >Maybe</option>
                                           </select>
                                        </li>
                                        <li>
                                                <label for="AnyQuestions" class="description" >Any Questions Or Suggessions </label>
                                                
                                            <textarea name="AnyQuestions" id="AnyQuestions" class="element textarea large"></textarea> 
                                        </li>

                                        <li>
                                                <label class="description" >Do You want to receive special offers. Please Select One</label>
                                                <input type="radio" name="opinion" value="1" />
                                                <label>Yes</label>
                                                <input  type="radio" name="opinion" value="2" />
                                                <label> No </label>
                                        </li>
                
                                        <li class="buttons">
                                                <input  type="submit" name="submit" value="Submit" />
                                        </li>
                                </ul>
                        </form>