javascript form validation won't return true

Trying to learn JS and seem to be coming along okay, but getting stuck on this form validation... It should validate that text boxes are not left empty or with the default value. Can get alert to pop up when validation returns false, but after entering info into the fields, the form does not return true to submit..

Any help is appreciated. See code below:

**THE SCRIPT**

function validateFunc() {
                var nameField = document.forms[0].visitor_name.value
                var emailField = document.forms[0].email.value
                var phoneField = document.forms[0].phone.value
                var areaField = document.forms[0].area.value
                if (nameField || emailField || phoneField || areaField === "") { 
                    window.alert("Please fill out all fields!");
                    return false;
                    }
                else {
                    return true                 
                }
            }


**THE FORM:**

<form action="FormProcessor.html" method="get" enctype="application/x-www-form-urlencoded" onsubmit= "return validateFunc()">
            <p>Name<br />
                <input type="text" name="visitor_name" size="50"/ value="Enter your name" onclick="if (this.value == 'Enter your name') this.value='';">                
            </p>
            <p>E-mail Address<br />
                <input type="text" name="email" size="50" value="Enter your email address" onclick="if (this.value == 'Enter your email address') this.value='';"/>             
            </p>
            <p>Phone<br />
                <input type="text" name="phone" size="50" value="Enter your phone number" onclick="if (this.value == 'Enter your phone number') this.value='';"/>               
            </p>
            <p>Area of town<br />
                <input type="text" name="area" size="50" value="What area of town are you interested in?" onchange="noEmptyBoxes()" onclick="if (this.value == 'What area of town are you interested in?') this.value='';"/>                
            </p>
            <p>Property
                <select name="property_type">
                    <option value="unselected">Select a property type</option>  
                    <option value="condo">Condos</option>   
                    <option value="single">Single Family Homes</option> 
                    <option value="multi">Multifamily Homes</option>    
                    <option value="mobile">Mobile Homes</option>    
                    <option value="land">Land</option>  
                </select>
                Sq. feet <input type="text" name="feet" size="5" value="???" onclick="if (this.value == '???') this.value='';"/>                
            </p>
            <p>Bedrooms <input type="text" name="bedrooms" size="5" value="???" onclick="if (this.value == '???') this.value='';"/>
               Maximum Price <input type="text" name="price" size="12" value="$$$" onclick="if (this.value == '$$$') this.value='';"/>              
            </p>
            <p>How should we contact you?
                <input type="radio" name="contactHow" value="call_me"/>Call me
                <input type="radio" name="contactHow" value="e-mail_me"/>Email me               
            </p>
            <p>
                <input type="submit"/>
            </p>
        </form>