Form Validation with JavaScript

<form name="form-validate" method="post" action="">
    <input type="text" name="name" />
    <input type="text" name="email" />
    <input type="submit" name="reg" value="Done" id="theclicker">
</form>

function restValidation() {
    valid = true;
    if ( document.form-validate.name.value == "" )
    {
        alert ( "Please fill in the 'Your Name' box." );
        valid = false;
    }
    return valid;
}
 
function doValidation(){
var send = document.getElementById('theclicker');
send.onclick = restValidation;
}
  
window.onload = doValidation;

function restValidation() {
    if ( document.form-validate.name.value == "" )
    {
        alert ( "Please fill in the 'Your Name' box." );
     }
}

onblur="validate(document.formName.fieldName.value) ;"

function validateEmail ( f ) {
  if ( isEmail ( f.email_address.value ) == false )
  {
    alert ( "Please enter a valid email address." );
    f.email_address.select ( );
    return false;
  }
  return true;
}

function isEmail ( string ) {
  if ( string.search(/^\w+((-\w+)|(\.\w+))*\@[A-Za-z0-9]+((\.|-)[A-Za-z0-9]+)*\.[A-Za-z0-9]+$/) != -1 )
    return true;
  else
    return false;
}

...

<form method="post" action="script.php" onsubmit="return validateEmail(this)"> ... </form>

<form method="post" action="script.php" onsubmit="return validate(this)"> ... </form>

function Validate()
{
    if (document.form1.first_name.value == '') 
    {
        alert('Please fill in your first name!');
        return false;
    }
	else if (document.form1.last_name.value == '') 
    {
        alert('Please fill in your last name!');
        return false;
    }
    else if (document.form1.email.value == '') 
    {
       alert('Please fill in your email address!');
       return false;
    }
	
	else if (document.form1.phone_number.value == '') 
    {
        alert('Please fill in your phone number!');
        return false;
    }
	else if (document.form1.user_type.value == '') 
    {
        alert('Please fill in your relevant user type!');
        return false;
    }
	
	else if (document.form1.username.value == '') 
    {
        alert('Please fill in your relevant username!');
        return false;
    }
    else if (document.form1.password.value == '') 
    {
       alert('Please fill in your desired password!');
      return false;
	}
	
	
     
    else if (document.form1.password_confirmation.value == '') 
    {
       alert('Please fill in your password again for confirmation!');
      return false;
    }
    else if (document.form1.password.value != 
    document.form1.password_confirmation.value) 
    {
        alert("The two passwords are not identical! "+
        "Please enter the same password again for confirmation");
        return false;
    }
    	
     else{
		 alert('You are successfully registered');
	 }
}

 <input type="submit" name="submit" value="Register User" onClick="return Validate();" class="attribute1" />

  } else if ( isEmail ( document.form1.email_address.value ) == false ) {
    alert ( "Please enter a valid email address." );
    return false;
  } else {
    alert('You are successfully registered');

  } else if ( !document.form1.email_address.value.match( /^[a-zA-Z]+$/ ) )  ) {
    alert ( "Please enter letters only." );
    return false;
  } else {
...

var answer = confirm( "Are you sure?" );

if ( answer == true ) {
  // yes
} else {
  // no
}

	if ( document.sapquote.loaddock-origin.selectedIndex == 0 )

<tr><td colspan=2 width="525" align="center">
<a class="form">Please let us know how you learned about us.<br></a></td></tr>
<tr>
<td colspan=2  width="525" align="center" class="form">
<select id="dropdown1" name="dropdown" onchange="display(this,'Google Search','Yahoo Search','Bing Search');" size="1" style="width:320px; font-size:11px; font-weight: bold; color: #686363;">
<option>Please select:</option>
<option value="Google Search">Google Search</option>
<option value="Yahoo Search">Yahoo Search</option>
<option value="Bing Search">Bing Search</option>
<option value="Other">Other</option>
</select>&nbsp;*
</td>
</tr>
</thead>


<tbody id="Google Search" style="display: none;">
<tr>
<td class="form" align="right"><br><br>Keywords used for search <font color="red">(Required)</font>:&nbsp;&nbsp;</td>
<td class="field"><br>
<input type="hidden" class="tbox1" id="textfield14" name="googlekey" size="40" value="-" />
<input type="text" class="tbox1" id="textfield14" name="googlekey" size="40" value="" /></td>
</tr>
</tbody>


<tbody id="Yahoo Search" style="display: none;">
<tr>
<td class="form" align="right"><br><br>Keywords used for search <font color="red">(Required)</font>:&nbsp;&nbsp;</td>
<td class="field"><br>
<input type="hidden" class="tbox1" id="textfield15" name="yahookey" size="40" value="-" />
<input type="text" class="tbox1" id="textfield15" name="yahookey" size="40" value="" /></td>
</tr>
</tbody>

    if ( document.contact_form.dropdown.selectedIndex == 1 && document.contact_form.googlekey.value == ""  )
    {
        alert ( "Please fill in the googlekey field" );
        valid = false;
    }

errorMessage += "Please select your Age.\n"

if ( !document.contact_form.surname.value.match( /^[a-zA-Z- ']+$/ ) || document.contact_form.surname.value.length > 30 ) {
  alert ( "Please enter your surname." );
  valid = false;
}

function validation(){
		
		
		valid = true;
		
		if (document.myForm.name.value ==""){
		
		alert("Please enter your name");
		valid = false;
		}
		if (document.myForm.lastname.value ==""){
		
		alert("Please enter your lastname");
		valid = false;
		}
		if (document.myForm.address.value ==""){
		
		alert("Please enter your address");
		valid = false;
		}
		
		return valid;